Tent Pegging is a sport dating back centuries. A skill originally used in warfare, tent pegging is done by galloping through the enemy's camp and tearing out his wooden tent pegs with a lance, causing the tent to collapse on him, at which point you can trample him more easily.
Nowadays tent peggers gallop down a level, trimmed field and skewer little wooden stakes out of the ground (no tent involved). More info on the contemporary version in the USA here.
This mini documentary (a few minutes long) clearly explains and demonstrates the sport.