The Celtics suffered a huge blowout loss to the Raptors on Tuesday night.
It means Boston and Toronto have tied the regular season series, but continues a poor run of form for the Celtics.
They have now lost five of their last seven games and they're dropping further away from their rivals at the top of the Eastern Conference.
Stevens, who has so often been able to get his Celtics side out of trouble in past seasons, he cut a frustrated figure all year long.
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And the performance against the Raptors was clearly too much for the usually composed head coach.
Boston picked up just 13 points in the second quarter and towards the end of the half, Tatum picked up a technical foul for a rather innocuous wave at the referee.
The 20-year-old wasn't happy with a foul call on him and as he jogged away he just softly waved his arm in the direction of referee J.T. Orr.
The official swiftly blew up for the technical and then got an earful from Stevens was left fuming at the call.
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Stevens was caught on camera shouting towards the official for the technical foul on Tatum and he wasn't happy.
"JT!" Stevens shouted.
"Airpunch, he loses his mind, that's one thing.
"He waved!
"Oh, everybody saw it. F***, who cares?"