Checking
Hockey is considered one of the most physical sports there
is. Players check each other at full speed and hold
nothing back. A player with a mass of 90 kg and moving
at 8.9 m/s has a kinetic energy of 3564 joules. If
that same player ran into a player of the same mass and
opposite velocity the impact would have a stopping force of
3204 Newtons. The stopping force in this circumstance
is found by dividing the change in momentum by the time of
the check taking place which is assumed to be a quarter of a
second. 
http://giphy.com/gifs/lakings-nhl-hockey-la-kings