Wordnet 3.0
NOUN (1)
1. 
 (American football) a catch of a punt on the fly by a defensive player who has signalled that he will not run and so should not be tackled; 
The Collaborative International Dictionary of English v.0.48:
Fair catch \Fair catch\ (Football)
   A catch made by a player on side who makes a prescribed
   signal that he will not attempt to advance the ball when
   caught. He must not then be interfered with.
   [Webster 1913 Suppl.]
WordNet (r) 3.0 (2006):
fair catch
    n 1: (American football) a catch of a punt on the fly by a
         defensive player who has signalled that he will not run and
         so should not be tackled