What's a "Swim move"?

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Originally posted by ChuckElias
Positioned this way, if B1 puts an arm up in front of A1, he has pretty good defense against the entry pass. If A1 then knocks down B1's arm, that would be a "swim stroke".
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I don't think I can describe it better, but now I need some clarification.

If A1 swims B1's arms per the above, then foul on A1.

However, exact same situation, if A1 were to reach for an incoming ball and contact arm-to-arm with B1 (preventing a catch), then we would call B1 for a foul wouldn't we?