http://legalinsurrection.com/2013/06/zimmerman-case-the-five-principles-of-the-law-of-self-defense/
The principle of Innocence refers to the notion that a person who initiates a conflict should not later be permitted to justify his use of force as self defense. It is this principle that is captured in Florida statute 776.041. It is, however, possible for the initial aggressor of a conflict to regain his “innocence” under certain circumstances., and thereby regain his right to justifiably use force in self defense
What I expect we will see at trial with regard to the principle of Innocence is the State arguing that Zimmerman engaged in conduct of a nature sufficient to qualify as “aggression”. The defense will respond that nothing Zimmerman did could reasonably qualify as an act of “aggression,” and at the same time that even if he did engage in such conduct he nevertheless “regained his innocence” afterwards.
From the same web page:
“In all states, however, if the unarmed attack is of such ferocity that it nevertheless raises a reasonable fear of death or grave bodily harm, the use of deadly force in self defense would be justified.”