Paul Pierce got slapped in the head by Omri Casspi earlier in the contest between the Sacramento Kings and the Washington Wizards, and it became clear a few moments later that Pierce did not appreciate the act.
Pierce got his revenge on Casspi when he pushed the Kings small forward from behind right into the front row behind the baseline. Casspi is a big man, so he was bound to do some damage barrelling into the crowd - which happened to include a little girl who got the brunt of the blow.
The girl seemed alright, but was clearly rattled. Pierce must have felt awful, and it only got worse for him when the crowd saw the result of the push and began to boo him ferociously.