What's important is what Zimmerman thought about the injuries. He thought that if the beating continued, his life would have been in danger.
The Trayvonbots want Z to have waited until the injuries WERE life threatening to act, and which point it was probably too late.
A mere hairline skull fracture can easily have severe consequences. If multiple blows involving hard objects have already caused bleeding on both sides of the head, you’re not far from irreversible damage.
Have to wonder if the defense is trying to throw this - either as a spiteful “I can’t win an unwinnable case”, or to induce race riots.