The British Tent Pegging Association have an excellent website (see this World War One recruitment film featuring the sport in this Pathé news clip – “The Army’s ripping fun old chap, do join!” – and another clip from the 1930s). It’s very friendly and you can learn a little about various teams, some military, and others, like Sarah’s “Pink Fairies” team, less than martial.
I had to go to Wikipedia to understand what was actually going on:
The specific game of tent pegging has a mounted horseman riding at a gallop and using a sword or a lance to pierce, pick up, and carry away a small ground target (a symbolic tent peg) or a series of small ground targets.
The broader class of tent pegging games also includes ring jousting (in which a galloping rider tries to pass the point of his weapon through a suspended ring); lemon sticking (in which the rider tries to stab or slice a lemon suspended from a cord or sitting on a platform); quintain tilting (in which the rider charges a mannequin mounted on a swivelling or rocking pedestal); and Parthian (i.e., mounted) archery.[1]
And:
The most widely accepted theory[5] is that the game originated in medieval India as a training tool for cavaliers facing war elephants. A cavalier able to precisely stab the highly sensitive flesh behind an elephant’s toenail would cause the enemy elephant to rear, unseat his mahout, and possibly run amok, breaking ranks and trampling infantry.
The term “tent pegging” is, however, certainly related to the idea that cavaliers mounting a surprise pre-dawn raid on an enemy camp could use the game’s skills to sever or uproot tent pegs, thus collapsing the tents on their sleeping occupants and sowing havoc and terror in the camp. However, there are few reliable accounts of a cavalry squadron ever employing such tactics.
Poor elephant! Imagine!
The best turn-out (in both senses) goes to the Royal Tent Pegging Club of Pakistan, who are really rather magnificent (and have better music, *ahem*):
* Yes, Flashman was a practitioner of the game, although knowing him, only in a peaceful setting with plenty of admiring memsahibs on hand.