An odd number of players, usually about 11 people and over, get into pairs, with one on their own. You then sit in a circle, with one person in each pair being behind the other one. The person on their own then will call out a condition, like "All those who are wearing red", or "All those who have a pet cat". The people on the inside then have to try to get to the lone person. Their partner has to try to stop them in basically any way possible. If you get to the person, you have to kiss them on the head to prove it. After every round, you (in some variants of the game), swop with your partner in order to have a turn at the other role.
There are few rules- no biting, no kicking in the nuts, no strangling... basically nothing that will cause REAL pain. Other than that, anything is allowed!