Kill the Man with the Ball is a game mode in which the goal is for the player to hold onto a "ball" for as long as possible.
The player attempts to hold the "ball" (which is actually a human skull) until reaching the target time without dying. An orange circle will appear on the motion sensor indicating the location of the person with the ball currently in posession. It is impossible to cause harm while carrying the ball, and the holder is much slower than usual. Usually, the best way to deal with an attacking enemy is to drop the the ball and fire upon them.