One thing I have noticed while watching "some" mlb hitters is that they get their back elbow back and above their hands during the stride. The elbow seems to reach its highest point (back and above hands) at toe touch. Bryce Harper for example, I believe does this. When the elbow is up and behind the hands while hip/shoulder rotation begins it forces the hands to stay connected to the shoulders longer until the rear elbow begins to slot. The hands are briefly locked into this position and can not physically drop until the back elbow gets below the hands. So as the shoulders turn, the rear elbow being high and behind hands moves the hands towards the ball as the back elbow slots. The high back elbow position at toe touch also seems to move the hands slightly up when the back elbow is trying to slot during shoulder rotation. This slight upward movement of the hands also seems as if it would help prevent bat drag.
Let me know what you think about this observation.
Thx,
BatDragon