Case in point: 

An Assistant Coach for the Jets Intentionally Tripped a Dolphin's Player Yesterday

During yesterday's game between the Jets and the Dolphins, a strength coach for New York named SAL ALOSI intentionally stuck his knee out on the sideline and tripped Miami defensive back NOLAN CARROLL.

Carroll fell down, and stayed down, then limped off the field under his own power.  But it must not have been too serious, because Carroll eventually returned to the game.

It's hard to see the trip, even in slow motion.  But it was definitely on purpose, and Alosi later issued an apology.