Zimmerman said he soon hit the ground.
"He started bashing my head into the concrete sidewalk," Zimmerman told Hannity. "As soon as he broke my nose, I started yelling for help because I was disoriented and he started slamming my head into the concrete."
Ambulance workers who treated Zimmerman on the night of the shooting told a court that Zimmerman's head was covered in blood after the shooting, and that the lacerations on his head "would probably need stitches."
Zimmerman's lawyers have tried to establish that their client might have thought he had suffered a "life-threatening injury."
Zimmerman's father has identified his son's voice as the male voice yelling for help in the background of a 911 call recording that was played in court.
Zimmerman said he shimmied to get onto the grass to avoid having his head hit the concrete. With Martin punching him, "cursing, telling me to shut up and, finally, he told me he was going to kill me," Zimmerman told Hannity, his movements exposed his gun under his jacket.
"He said, 'You're going to die tonight,'" Zimmerman told Hannity.
Zimmerman said he soon believed he felt Martin's hand moving for the gun, but Zimmerman reached it first.
Zimmerman told Hannity he'd like to have the opportunity to apologize to Martin's family.
"I would tell them that, again, I'm sorry," he said.
"My wife and I don't have any children," he said. "I have nephews that I love more than life. I love them more than myself. And I know when they were born, it was a different unique bond and love that I have with them. And I love my children even though that they aren't born yet.
"I am sorry that they buried their child," he added. "I can't imagine what it must feel like. And I pray for them daily."