This is likely a question for SW22, but if anyone has an answer let me know...
So this whole thumb push/roll under thing, which is like turning your wrist when punching...is this what is happening in a pro level baseball swing too before the wrists turn over to follow through with the bat? I've never thought of rolling "under" near contact before, just rolling your wrists the other way for the follow through motion.
For example, watch the left wrist of Bautista (pretend it's a LHBH drive with 600' of power) from 0:33-0:35 in the video. You can see it roll under at/through contact, and then the wrists turn over the other way to follow through the swing.