Well, that escalated quickly.
The reason? As many players tend to do, Johnson wanted a touch of the ball after it went through the net following a free throw. Official David Jones wouldn't give it to him. Johnson and Jones engaged in a small tug-of-war over the ball, with Jones using his whistle to settle the stalemate.
Jones hit Johnson with a technical, Johnson obviously took exception and said the magic words to get hit with another. But instead of making a tidy exit, Johnson threw his mouthpiece at Jones, hitting him square in the back.
The way Toronto coach Dwane Casey drops his head during the explanation says it all. SMH, for sure.
Not to condone Johnson's actions, but sometimes you can at least see where the players are coming from in their frustrations with officials. Why wouldn't Jones give him the ball? That's a pretty standard practice thing at the free throw line. The one thing players won't stand for when it comes to officials is not being fair. And likely in Johnson's point of view, Jones was singling him out and showing him up.
Still, Johnson probably doesn't escape this without a suspension. It's one thing to get tossed for silly reasons, but it's a whole other to completely lose your head and throw something at a ref.