They say a flinch by a pitcher is a balk. Then why isn't a balk called on K-Rod when he pitches for the Mets? With a man on first base, he comes to his set position, he then rocks back and forth, even lifts his front heel although his foot technically stays on the ground. Shouldn't this constitute a start of his delivery and therefore be a balk? I was told he does it every pitch so its not a balk. Why doesn't an umpire call a balk the first time he does it in a game? The umpire can't assume he's going to do it on the next pitch and therefore not call it? Also, what would constitute a flinch by a pitcher? Does it matter if its a leg, knee, shoulder, etc.? Thanks for your help.
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