He could have blown his whistle, but that would have been way less athletic.
In last night's game against the Toronto Raptors, Brooklyn Net Kris Humphries was about to take a free throw when NBA ref Courtney Kirkland realized he had given the ball to Humphries too soon. So he took things into his own hands.
Here it is in video form:
Source: youtube.com
H/T HyperVocal.