Swinging Elbows

[carldog]

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?