Jump ball mechanics -3 man
 

R tosses ball and tip goes straight back where there is a scramble to gain possession at corner of U2 sideline and division line. Away from the scramble, at the free throw line at U2 end of court A1 punches B1. (Flagrant foul used for best effect)

Who is responsible for calling the foul?
What are the responsibilities of each official?
How would we pregame this scenario?

Anyone that sees this foul, should call this foul. You really do not have defined coverage areas until you get into the half court. I do not know that I would necessarily pre-game this, but I do not think you want to get into defining something specific when this is an unusual situation. Just call what you see even if it is the official the farthest from the play.

Peace

Well I suppose it's highly unlikely U2 will see the punch. But, either way, whoever sees it, call it. If anything non-basketball happens, no matter where it occurs, it's the officials job to call it.