Illegal motion or shift?

[bisonlj]

How about this situation?

Team A lineman has a slight twitch before the ball is snapped but it by itself is not something you are gonig to flag. You might talk to him and remind him he is to remain set but if you flagged that everytime you saw it, you'd have flags all night. Good judgment does come into play in several situations during a game.

Now let's say you determine that exact same twitch is what caused a B player to encroach. Would you penalize B for encroachment or would you penalize A for a false start?