Want to see a head coach freak out? Don’t watch a Boston Celtics game.

That’s usually the case, as Brad Stevens is about as level-headed as they come. But the normally mild-mannered Celtics coach surprisingly broke character in the first half of Tuesday’s game against the Milwaukee Bucks.

After Isaiah Thomas’ failure to pick up Khris Middleton led to the Bucks sharpshooter knocking down a 3-pointer, Stevens called a timeout and ripped into Thomas as he approached Boston’s bench.

Brad Stevens is furious at Isaiah Thomas after that Bucks 3-pointer. Called timeout and stomped onto the floor to yell at him. — Adam Himmelsbach (@AdamHimmelsbach) November 11, 2015

https://vine.co/v/elDB92pJ2vn

https://vine.co/v/elp3MKpEwda

You know you’ve done something wrong when one of the calmest coaches in the NBA is ripping into you.

Fortunately for Thomas, though, it appears Stevens’ moment of fury was brief.

Brad did follow this up with an atta-boy butt tap, so even angry Brad is sorta nice https://t.co/hbIOxPMEu2 — Adam Himmelsbach (@AdamHimmelsbach) November 11, 2015

Just don’t let it happen again, Isaiah.

Thumbnail photo via Brian Spurlock/USA TODAY Sports Images

Thumbnail photo via Boston Celtics coach Brad Stevens coaches on the sidelines against the Indiana Pacers at Bankers Life Fieldhouse. Indiana defeats Boston 100-98.