[Updated at 11:37 a.m. ET]
Osterman says Zimmerman looked down to get his phone out of his pocket, and when he looked back up, "the punch came squarely in his face." Zimmerman says he stumbled to the ground and Martin straddled him.
"His knees were up somewhere near his chest or up near his armpits, and he was beginning to punch him," said Osterman.
[Updated at 11:34 a.m. ET]
Osterman has written a book about the case and quoted Martin as saying, "Do you have a problem?" Osterman says that there was an expletive, "mother [expletive]," but that his publisher wanted him to take it out of the book because it was graphic.
[Updated at 11:32 a.m. ET]
There were two phases of contact, according to Osterman: When Zimmerman first saw Martin and pulled into the clubhouse parking lot, and the second one, when Martin walked down a side street and Zimmerman followed him with his car and lost sight of him, getting out of his car to find an address.
[Updated at 11:30 a.m. ET]
Martin circled the car, according to Zimmerman. Osterman says they looked at each other and Zimmerman briefly lost sight of Martin.
[Updated at 11:28 a.m. ET]
"Someone who usually looks through a neighborhood while it's raining -- it's suspicious," said Osterman. Zimmerman told him he called the nonemergency number.
[Updated at 11:26 a.m. ET]
Osterman recounts the story Zimmerman told him the day after the shooting. Zimmerman was going to Target to get lunches for the week. He saw someone he didn't know walking through homes and looking into windows.
[Updated at 11:24 a.m. ET]
The prosecution has called Mark Osterman to the witness stand.
"Would you consider him a very good friend?" asked prosecutor de la Rionda.
"The best friend I've ever had," said Osterman.
[Updated at 11:22 a.m. ET]
The jury is being seated.
[Updated at 11:04 a.m. ET]
The judge has recessed court for a 15-minute break.
[Updated at 11:03 a.m. ET]
Serino says the blood may have been going back down Zimmerman's nose and throat and that it may have dripped down once he stood up.
"Could the attempt to suffocate literally be momentary as well?" asked de la Rionda.
"Yes sir," said Serino.