You could argue that the block on A2 is legal if he qualifies as a "potential blocker." We had this discussion in another thread a while back. If A2 isn't presenting himself as a blocker, then you would flag B for Illegal use of hands, 9-2-3D. Sit 9.2.3A covers a situation similar to this (2004 Fed books- haven't received 2005 yet
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Then from here I agree with MJT, but depending on the severity of the hit, A4 might not be ejected.