As long as the Team B player has re-established himself inbounds, he is free to do anything (otherwise legal) he wants to do.
But, let's focus on a Team A player.
If a Team A player goes OB voluntarily, then re-establishes himself inbounds, he has committed a foul for an "illegal return." However, anything otherwise legal that he does is...well, legal. If he is otherwise eligible to touch the ball, he may still touch the ball. He may block. He may tackle the BC. But, when the down is over, the penalty for his foul for returning to the field will be completed (accepted, declined, or offset).
If he is blocked OB, but returns inbounds as soon as he possibly can, then he has NOT fouled.
In either case, he must re-establish himself to avoid making the ball dead if he touches it.
Robert
