It really wasn't even close. Team B player grabs defensive rebound, is closely, cleanly harassed by a Team A player so as to prevent a quick outlet pass. Team B guy tucks ball under his left arm, then violently swings his right elbow through an 90 degree arc and at chin level, just missing Team A player's jaw. No call.

Ref takes the opportunity to explain his No Call to Team A coach at next dead ball.

What could the explanation have been?

Might have been like this
 

Coach: "come on you've got to call that"

Ref: "you're right, coach I missed it! I'll get him next time"

Really the only thing in the referee's corner is that he did not make contact at least.

Thanks
David