Stand in a circle. One person announces, "I am Mr. Hit!" Mr. Hit begins walking directly (but slowly, at first) toward another person in the circle, with his hands out in front of him. If he touches (hits) the person, they are "out" and must leave the circle. The only way the intended victim can stop Mr. Hit is to call out the name of another person in the circle before any contact is made. No fair running away.
Once a name is called out, that person instantly becomes Mr. Hit and begins advancing on a victim. (He doesn't have to announce that he is Mr. Hit after the first time.) Again, the only way the victim can save himself is by calling out a name.
Continue play until all but two people have been eliminated. it gets harder and harder, because as people are "out" the fund of names grows smaller. You can't say the name of a person who is out -- it must be someone who is still in the circle. It sounds easy, but it isn't. It is very difficult to think with Mr. Hit bearing down on you.
Some groups find that they have to change the name of the game to "Mr. Tap" to avoid injury.