Fair escape rules are a feature of many Dramatist live-action role-playing experiences (I hesitate to call them games). The idea is that player skill and athleticism should have as little of an impact on the game as possible: the fact that I'm a 300-pound lump shouldn't keep me from playing a clone of Spiderman. In particular, it might be unsafe to make me run, jog, or flee in terror: some players might not be able to, say, run a quarter mile up hill, dodge into a parking garage, leap down three flights of stairs in four mighty bounds, grab a railing, flip upside down, and drop the last twenty feet to the ground, flawlessly evading their pursuers. But if an athletic player is chasing them, that might be the only way to get away.
Hence, fair escape: if a player can get out of ZOC of opponents or enemies, he can call fair escape. The game pauses briefly while he goes away, then resumes with his opponents unable to follow him. In some variations, it turns into a mechanical, tabletop-style resolution mechanic to see who's faster.
This rule is unfortunately often abused, resulting in physically impossible situations. It very rarely shows up in Gamist live-action RPGs, which tend to view player skill at athletics as just as valid a playing piece as player skill at politics or Nerf gunplay.