For the most part, hitters really can't control thier BA on balls in play(BABIP), i.e. not HR's or K's. Ichiro is the obvious exception, and speedsters/bunters tend to have a higher BABIP. Essentially you can use BABIP, along with your knowledge of what type of hitter you're comparing, to tell if a hitter has been lucky or not.
After tonight, Rowand has a BABIP of .250 compared to a league average of .297 -- His average should come up. Duh
Crede, who you might think with his recent hot streak may be a little lucky, has a BABIP of .298 or essentially league average. -- His average hasn't been attributed to luck. Surprise.
Last year Rowand had a BABIP of .341 compared to a league average of .303, and Crede had a BABIP of .247. In other words, crede is a good candidate for a rebound, and Rowand is a good candidate for regression.
Formula for BABIP = [H-HR]/[AB-HR-K] -- Obviously not everything can be explained by subtracting homeruns and strikouts, but it's a good indicator.