The fight broke out in the upper seats of the Garden, while the Celtics were in the middle of a big rally in the game.
An anonymous video of the fight, posted to DeadSpin.com, shows an altercation the poster says led up to the stabbing.
Two men can be seen getting into an argument, one in a white jersey and the other in a dark-colored Rondo jersey with his back to the camera. The men can be heard and seen exchanging words and gestures, which is when it appears that the man in the white jersey pulls out a knife and motions to fight. At the same time, another fight breaks out in the same area and people start running.
Boston police say that a 21-year-old man was taken to the hospital after being stabbed in the stomach. His injuries are non-life threatening.
No arrests have been made. Police are searching for a suspect in the stabbing, who they say fled after the assault.
The Celtics won Wednesday night's game in a 95-92 victory.
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