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Some left handed pitchers, Jamie Moyer, for example, lift their leg from the stretch and, in those first moments, "read" the base runner: If the runner takes off they throw to first, if not, they throw home.
Maddon's point is that Hamel's is not one of these pitchers. He throws harder than Moyer and one of the reasons why is he uses his lower body more. It is harder to read if you "load" your lower half as Hamels does. So, while Moyer's center of gravity will not be moving towards home plate when he throws to first, Hamels' was, and that is what Maddon means when he says, "He's going home all the way." If your body is moving towards home plate, it is much harder to step towards first base. It is still possible, and Welke claimed he saw Hamels step about a foot towards first base, which is why he didn't call a balk.
Scouting reports would have told the Ray's staff that Hamels was not a "reader" and so they told their base stealers to "go on first movement." This is not something they would likely try with Moyer, but was worth the risk with Hamels. Maddon went out to discuss this so that the next time Hamels pitches the home plate umpire will watch his right foot more closely to make sure it is stepping towards the base.