Referee Joey Crawford leaves Mavericks-Clippers game with knee injury

NBA games are a physical strain on the refs, too, and every once in a while, something goes wrong:

That's veteran ref Joey Crawford pulling up lame while shuffling down the floor in the first half of Mavs-Clippers. Crawford appeared to be in quite a bit of pain after the misstep:

Joey Crawford in sheer pain from injury https://t.co/Ney3B5T0ZX

— AP (@Ananth_Pandian) January 10, 2015

Crawford was helped to the locker room, and is out with a knee injury:

Joey Crawford has a right knee injury and is doubtful to return

— Dan Woike (@DanWoikeSports) January 10, 2015

The two remaining referees -- Leroy Richardson and Derrick Collins -- will have to handle the rest of the game on their own.