We all know Mune has been horrendous for the past month. But I actually wanted to know why.

The Slump
August 19th, 2026 was Murakami's first MLB game where he didn't generate a single 3 true outcome. No strikeouts, no walks, and no homers. He put a ball in play every AB that day against the Cubs. And that apparently broke him. Because since August 19th, Murakami has only had 9 hits. That's unheard of for someone that plays everyday (and was batting 2nd in the lineup until recently).

His slash line during that time: .096/.248/.170 in 113 PA.
For comparison, in Drew Romo's last 114 PAs with the Sox, his slash line is: .129/.221/.198.

So how did a guy who was hitting .234/.372/.545 in his first 393 PA turn into of one of the worst hitting catchers in baseball history? Let's dive into the theories.

The Hamstring Injury
I've seen a narrative where the hamstring injury caused the slide. I don't think that's true. Mune had about a 2 week stretch where he needed to get acclimated to major league pitching again after taking 6 weeks off. In his first 10 games back he hit .176/.364/.294 with no homers. From that point on until August 19th, he hit .241/.359/.609 with 9 home runs. He was basically back to what he was doing pre-injury.

But let's say something did change. Maybe the injury changed his swing. Maybe the home run derby did. Whatever your theory is, let's set a baseline.

Before injury: .240/.378/.560, 94.2 MPH EV, 15 degree launch angle, 73.3 MPH bat speed, 18 degree attack angle, 7.8 feet swing length, 35 degree swing path tilt, 0 degree attack direction.
10 games after injury: .176/.364./294, 91.9 MPH EV, 20 degree launch angle, 74.2 MPH bat speed, 19 degree attack angle, 7.7 feet swing length, 36 degree swing path tilt, 4 degree opp attack direction.
After-injury hot streak (7/25-8/18): .241/.359/.609, 94.9 MPH EV, 19 degree launch angle, 70.6 MPH bat speed, 19 degree attack angle, 36 degree swing path tilt, 3 degree opp attack direction.

What's interesting here is that he was actually swinging the bat harder during his first 10 games back post injury, but he wasn't hitting the ball anywhere near as hard. That's understandable since he probably had to get his legs under him after 6 week hamstring injury.

During his post injury hot streak, what stood out the most was his lower bat speed, yet much higher exit velos. You would expect lower bat speed to generate lower exit velos and less power, but that wasn't the case during this stretch. What may have accounted for this is that his barrels/PA went up about 3.6% over his pre-injury numbers. So he might have made a change to swing less hard in order to get better bat control. When you swing as hard as Mune, you don't need to try to hit it to the moon every time to hit for power.

What's notable here is the big increase in launch angle. Over a sample of about 150 PAs, things like that may change, but a 4-5 degree difference is very notable. The 1 degree rise in attack angle and swing tilt meant that he had a more uppercut swing during this stretch, which can attribute to the higher launch angle. But this is not always the case (as you will see later).

Another thing to note is the change in attack direction. Attack direction basically determines whether you are late (opp) or early (pull) on a swing. You actually want to be at 0 degrees, which is what Mune was at pre-injury. Post-injury, he was late on his swings, meaning he was hitting the ball deeper in the zone. You don't want this if you're a power hitter like him with an extreme upper cut swing. Because you're basically eliminating the optimal time in the zone with your bat path.

So while Mune did get back to his pre-injury production after his hamstring injury, there is a change to his swing profile. It's fairly minor, but the change in launch angle and attack direction are definitely worth noting. I think the fact that he got back to pre-injury production after the injury means that alone is not the reason for his slump.

No True Outcomes
I'm going to use the 8/19 date as a cut-off because it's kind of fitting that not striking out, walking, or homering for a single game would break a hitter like Mune. But it's also the start of a gigantic cold streak for him, where he would hit .085 with no homers over the next 71 PA.

Over that stretch, these were his numbers: .085/.239/.102, 91.8 MPH EV, 16 degree launch angle, 73 MPH bat speed, 21 degree attack angle, 38 degree swing tilt, 1 degree pull attack direction.

Now compare this to the 3 week period before it. His launch angle drops while he starts swinging harder. His swing is now at the extreme bound of upper cut for a ML hitter. A 2-3 degree change in swing tilt mid-season is almost unheard of. The rise in attack angle is also pretty significant for an in-season change. He is also swinging earlier, perhaps opening up too much to try and catch up to velocity inside. This would leave him more vulnerable to outside pitches though.

Just from an anecdotal standpoint, I remember watching him during this time and thinking that he was simply popping up too many fly balls with extremely high launch angles. Homers he'd hit before were now deep fly balls that died at the warning track because they were simply hit too high. However, the data is telling us that he actually lowered his launch angle. That might have to do with him potentially rolling over on pitches from swinging early.

On September 5th, Murakami finally hit his 30th homer on a towering fly ball with a near 50 degree launch angle that barely made it over the left field wall. So slump over, right? Nope, the next 2 weeks would be more or less the same. Except his launch angle has somehow dropped even lower.

9/5-9/15: .114/.286/.161, 93.1 MPH EV, 9 degree launch angle, 70 MPH bat speed, 19 degree attack angle, 37 degree swing tilt, 6 degree opp attack direction.

So we've got a case of a power hitter trying to lift the ball more with a more upper cut swing, but it's actually resulting in a lower launch angle. He's also seemingly slowing down his swing more in recent weeks. I think the somewhat small sample could be the reason why you see the variance in bat speed, but it could also just be him tinkering with his swing to try and get right. The complete change in attack direction also means that he is now hitting the ball much deeper in the zone than before. If he looks late on outside fastballs, it's because he's got no chance to hit them with how late he is swinging.

What can we conclude from this so far? I think ever since his cold streak started, Mune has been tinkering with his swing, mostly trying to gain more loft to lift the ball. In the process, it seems like it broke his swing. He's now uppercutting more than ever, but is somehow hitting the ball at a lower launch angle. You usually wouldn't expect that combination. He's also consistently changing his swing to cover up for one weakness or another. The pull attack angle indicates he wanted to try and cover velocity while the opposite attack angle more recently suggests he wants to cover the low and outside breaking stuff.

League Adjustment
Another popular theory about Mune's demise is that the league has figured him out. This one may actually have some legs.

Prior to 8/18, this is how the league pitched Mune:

By pitch type: 28.8% 4FB, 5.8% cutter, 2.9% split, 14.7% sinker, 26.2% slider, 7.7% curveball, 2.6% knuckle curve, 11.2% change up.

Since then, this is how they're pitching him:

By pitch type: 25.7% 4FB, 9.1% cutter, 3.4% split, 10.5% sinker, 37.3% slider, 2.5% curveball, 11.2 % change up.

The general trend is that they've stopped throwing him high in the zone and have moved more to low and outside. They're throwing him less fastballs and way more stuff that moves. The jump in slider % is probably the most drastic one, with the cutter increase being 2nd. I'm thinking that's righties throwing more cutters inside to him as well as low and in sliders. I've also seen quite a few try to backdoor him with a slider/cutter/split/change low and outside, which is exactly where the hottest part of the heatmap is.

So there's an approach change for sure by the opposition and it seems like it has worked. But is this because they're attacking Mune's weaknesses or is this because of his swing change?

Here's Mune's zone profile by wOBA prior to 8/18:

He was more or less dangerous anywhere in the zone unless you threw him high and in. Also look at his numbers in the outside and low zone, it's actually one of his hotter zones. I don't think that opponents would have gotten away with the outside and low approach to Mune prior to his slump and swing change.

If you want a laugh, here is his zone profile since 8/18:


It's no wonder the advanced scouting caught up and they throw the ball low and outside to him now. But then again, his entire strike zone is cold unless you throw middle/low.

What Broke Mune?

I'm not a hitting coach. I don't have a great grasp on swing physics or swing paths. So in reality, I don't actually know. But I think from digging around on Statcast for a few hours a few things became clear.
1. The injury may have not directly caused his slump, but the time off made him alter his swing and timing. Murakami eventually adjusted to the new swing and timing to still produce like he did pre-injury.
2. Sometime around mid August, he drastically altered his swing to be more uppercut while also swinging earlier. This would cause him to go into a huge slump.
3. Around this same time, teams adjust and start throwing him low and away off-speed pitches.
4. Mune is now stuck in a cycle of tinkering where he's either trying to cover velocity or the low and slow stuff that pitchers are now spamming. No adjustment has worked thus far.

I think the good news that I got out of this is that I don't think Mune is incapable of getting out of this slump. The physical characteristics are all still there. He can still swing hard. He's still capable of hitting the ball hard. His swing and timing are just so jacked up that he can't do it right now. The way that pitchers are pitching him is because of the adjustments he made to his swing in August. I think his zone profile prior to the slump kind of proves that he can handle pitches in the strike zone when he's going right. But, because he's so out of it right now, pitchers will keep spamming what works until he proves he can hit it again. I just wouldn't expect that to happen anytime this season.

Absolutely great stuff, kudos! I think his bat path is so messed up. His hands obviously starts high, and then he immediately drops them a staggering amount. He also seems to have no confidence anymore, and it’s apparent in his body language.

The biggest question is whether he remains irreparably broken next year.

Certainly nothing’s getting fixed for this year, for both him and Kolson…heck, Braden, too.

but how can you possibly plan for 2027 with those three?

It’s hard to imagine Mune would just give up and go back to Japan and leave that $$$ on the table (as well as future FA dreams), but absolutely anything feels possible atm

Getting released or traded next mid season feel like equal likelihoods

Finally, there are going to be lots of questions about the hitting coaches/approach as well this off-season. Does it have a limitation, or even fatal flaw against competition outside the AL Central/West???

Ofc Vargas Peters Meidroth Antonacci Grichuk Bonemer Boston Smith all stood out on the positive side of the ledger.

But the rebuild feels like it’s still at a crossroads of sorts.

Kyle Teel getting back to 100% and playing like his second half 2025 version feels more critical than ever.

Edited 7 hours ago7 hr by caulfield12

The details are interesting, but I think that shows that pitching has adjusted and he hasn't been able to adjust back.

The off season will be interesting because does Getz still stand behind his extension talk? If Mune came to him at say a reduced FA price of 5/100 would he jump on it, or is he scared off now?

Post of the year. This is awesome.

2 minutes ago, southsider2k5 said:

The details are interesting, but I think that shows that pitching has adjusted and he hasn't been able to adjust back.

The off season will be interesting because does Getz still stand behind his extension talk? If Mune came to him at say a reduced FA price of 5/100 would he jump on it, or is he scared off now?

hmm that's a good question. I think a lot of the extension numbers prior were blow out of proportion. I think the 5/80-100 is about right for a power hitting 1B with little track record. I mean Alonso with like 6 years of track record got what, 5/150?

6 minutes ago, Squirmin' for Yermin said:

hmm that's a good question. I think a lot of the extension numbers prior were blow out of proportion. I think the 5/80-100 is about right for a power hitting 1B with little track record. I mean Alonso with like 6 years of track record got what, 5/150?

And this was like the higher/histest side I would do. Nothing longer than that, even when he was hitting.

Using only eyesight and not baseball expertise...I think Mune looks skinnier than he was at the beginning of the year! I know that isn't the cause for this disappointing second half but the other night I was watching and when he came to the plate I thought to myself "who is this skinny guy hitting"?!

Okamoto’s 4/$60 doesn’t seem all that far off.

33 homers and subpar defense at third…lower OPS overall than Mune but clearly on the upswing.

255 k’s had Murakami played out the full season is absolutely nuts, but had he maintained his earlier paces and not gotten hurt, would arguably now be at 40-45 homers and probably 210-225 k’s.

50 minutes ago, southsider2k5 said:

The details are interesting, but I think that shows that pitching has adjusted and he hasn't been able to adjust back.

The off season will be interesting because does Getz still stand behind his extension talk? If Mune came to him at say a reduced FA price of 5/100 would he jump on it, or is he scared off now?

No way in the world you extend him. Could easily be back in Japan in two years.

55 minutes ago, Squirmin' for Yermin said:

hmm that's a good question. I think a lot of the extension numbers prior were blow out of proportion. I think the 5/80-100 is about right for a power hitting 1B with little track record. I mean Alonso with like 6 years of track record got what, 5/150?

I want to say Pete was also 4 or 5 years older when he signed his deal.

What was the Sox record when Mune was injured?

Maybe his translator racked up millions of dollars in betting debts on a $75,000 salary.

42 minutes ago, Milkman delivers said:

Maybe his translator racked up millions of dollars in betting debts on a $75,000 salary.

People still believe it was the translator?

9 minutes ago, Squirmin' for Yermin said:

People still believe it was the translator?

Why else would he take the dive?

Playing in Japan isn't an easy move to MLB in the first year. There plenty of failures we ignore.

He could hit the ball basically in any part of the zone, but do we know how well he hits fastballs vs offspeed? Seems like he's having trouble picking up spin to me (based on how often he swings and misses on crap in the dirt). He also seems in between to a degree that paralyzes his decision making at the plate, which is why he's not swinging at some obvious strikes. Also I can't find it now but I saw a comparison of his setup and its very different now as compared to when he was hitting.

Basically, he's a complete mess and needs a reset.

5 minutes ago, almagest said:

He could hit the ball basically in any part of the zone, but do we know how well he hits fastballs vs offspeed? Seems like he's having trouble picking up spin to me (based on how often he swings and misses on crap in the dirt). He also seems in between to a degree that paralyzes his decision making at the plate, which is why he's not swinging at some obvious strikes. Also I can't find it now but I saw a comparison of his setup and its very different now as compared to when he was hitting.

Basically, he's a complete mess and needs a reset.

There are a few of things that might be happening here.

#1 Playoff race

#2 Pitchers have adjusted to his strengths AND weaknesses

#3 the MLB season is way longer and more intense than the Japanese one.

#4 the critics were right and he isn't good enough for MLB long term, which is why a lot of teams avoided him.

If I had to guess I would say mostly 2 with a decent amount of 3 mixed in. We will find out about 4 next year.

Guys go in slumps but Mune and Colson have to be suffering from bad mechanics, I’m not a hitting coach but the one we have for some reason can’t fix them. Hitting should be simple, see the ball, hit the ball but I’m wondering with all the information available to the modern day player is a bit much and the trend of swinging as hard as one can along with launch angles ruins some players, just look at the batting averages, there’s only 7 guys in MLB that are batting .300. Junior Caminero of the Rays leads the AL in homers with 41 and has one of the flattest swings in baseball but he does swing hard and manages to knock the ball over fences. I’m pretty sure it’s a lot harder to hit a baseball coming at you at 96 MPH with an uppercut swing versus a flat swing. This isn’t 16 inch slow pitch softball like we played in our youth when we had a huge ball and the time to meet the ball with an uppercut swing.

Edited 3 hours ago3 hr by The Mighty Mite

55 minutes ago, southsider2k5 said:

There are a few of things that might be happening here.

#1 Playoff race

#2 Pitchers have adjusted to his strengths AND weaknesses

#3 the MLB season is way longer and more intense than the Japanese one.

#4 the critics were right and he isn't good enough for MLB long term, which is why a lot of teams avoided him.

If I had to guess I would say mostly 2 with a decent amount of 3 mixed in. We will find out about 4 next year.

I wouldn't discount #1. This is the most meaningful professional baseball he's played (outside of the WBC, where he also has struggled). His teams in Japan were not good.

1 hour ago, almagest said:

I wouldn't discount #1. This is the most meaningful professional baseball he's played (outside of the WBC, where he also has struggled). His teams in Japan were not good.

That's fair as I have no idea what the rest of his professional experience consists of in terms of high stakes baseball.

26 minutes ago, southsider2k5 said:

That's fair as I have no idea what the rest of his professional experience consists of in terms of high stakes baseball.

Yakult was really good (2 Japan series appearances, 1 win) the years he won MVP (2021/2022). Outside of those two years they were 276–390–26. So he does have high level playoff experience and expectations, just not here.

Edited 1 hour ago1 hr by almagest

Thanks for the original post. As someone who coaches above the HS level, not baseball, I find the analytics of this to be fascinating.

3 hours ago, southsider2k5 said:

There are a few of things that might be happening here.

#1 Playoff race

#2 Pitchers have adjusted to his strengths AND weaknesses

#3 the MLB season is way longer and more intense than the Japanese one.

#4 the critics were right and he isn't good enough for MLB long term, which is why a lot of teams avoided him.

If I had to guess I would say mostly 2 with a decent amount of 3 mixed in. We will find out about 4 next year.

Kinda feel that both 1 and 3 are affecting his ability to deal with 2.

1 hour ago, southsider2k5 said:

The details are interesting, but I think that shows that pitching has adjusted and he hasn't been able to adjust back.

The off season will be interesting because does Getz still stand behind his extension talk? If Mune came to him at say a reduced FA price of 5/100 would he jump on it, or is he scared off now?

I should probably look at the heat maps by pitch type to see how they're throwing him pitches differently.