ambush!
Very much like tag, but emphasizing stealth. Everyone on the playground played, whether they realized it or not, whether they wanted to or not. The stalker had to sneak behind someone, push them to the ground and shout 'Ambush!' Should the person survive, they were the new stalker. This game fractured my kneecap.

'about as much use as a one-legged man at an arse-kicking party'
http://www.playgroundlaw.com
Lubcha's Website pick of the Fortnight.