Source: Woodcraft Folk Games Games Games

One person is the Untigger; everyone else stands frozen in place. The Untigger runs around the room, releasing people by "untigging" them. When untigged, players attempt to catch the Untigger and hold them in place to prevent them from untigging anyone else.

When the Untigger realises they will not be able to free anyone else, they can call out the name of a frozen player. That frozen player now becomes the Untigger, and the previous Untigger is frozen.

Continue until all players have been released or the game runs out of steam.