I have been reading Tim McCarver's book on baseball and I got to the hitting chapter. He said that most of the time when a hitter is struggling he is usually being over-aggressive. This means a guy like Frank Thomas feels like his timing is slow and is trying to compensate by getting his hands out faster and that is what makes him pop it up alot. With the aluminum bat in BP, Frank's hands get through the hitting zone much more quickly and it can help his timing and confidence. As Hawk would say, Frank is a strong man.