The NBA suspended the Toronto Raptors' forward one game on Tuesday for hurling the protective gear at referee David Jones following his ejection from Monday night's game in Portland.
The incident occurred in the third quarter of Toronto's 92-74 loss to the Trail Blazers when both Johnson and Jones tugged at the ball following a Portland free throw.
After Jones ejected Johnson and started to walk away, Johnson threw his mouthguard in Jones' direction.
Fellow players had to restrain Johnson before he was escorted from the floor.
He will miss Wednesday night's game at Air Canada Centre against the Brooklyn Nets.
Johnson said after the game he has a habit of rubbing the ball before handing it to the ref during free throws. While it appeared that the two had words, Johnson claimed nothing much was said.
He said he got frustrated when he wasn't given an explanation for the ejection.
"I guess the ref didn't let me have the ball so we kind of got into a tug of war," Johnson said Monday. "No words were really said and he rejected me out of the game and I kind of lost my cool from there."
Johnson is averaging 7.3 points and 5.4 rebounds this season. He finished the game with four points and four rebounds in just over 10 minutes.