The Collaborative International Dictionary of English v.0.48:

infighting \infighting\ n. [in- + fighting.]
   1. contention among members of the same organization (usually
      concealed from outsiders), sometimes of a bitter, intense,
      or prolonged character.

   Note: [Such infighting may lead to factionalism.] PJC]

   2. fighting, such as boxing, at close quarters.
      [PJC]

   3. rough-and-tumble, free-for-all fighting.
      [PJC]

WordNet (r) 3.0 (2006):

in-fighting
    n 1: conflict between members of the same organization (usually
         concealed from outsiders)
    2: boxing at close quarters