704.6  When defense not available.
  The defense of justification is not available to the following:
  1.  One who is participating in a forcible felony, or riot, or a duel.
  2.  One who initially provokes the use of force against oneself, with the intent to use such force as an excuse to inflict injury on the assailant.
  3.  One who initially provokes the use of force against oneself by one’s unlawful acts, unless:
  a.  Such force is grossly disproportionate to the provocation, and is so great that the person reasonably believes that the person is in imminent danger of death or serious injury or
  b.  The person withdraws from physical contact with the other and indicates clearly to the other that the person desires to terminate the conflict but the other continues or resumes the use of force.
[C79, 81, §704.6]
Forcible felony defined, see §702.11