This June 20, 2013 file photo, George Zimmerman listens as his defense counsel Mark O'Mara questions potential jurors during Zimmerman's trial in Seminole circuit court in Sanford, Florida
Sanford, FL -- A critical witness in the George Zimmerman second degree murder trial took the stand Friday and testified he believes he saw Trayvon Martin straddling the neighborhood watch volunteer in a mixed martial arts position he called "ground and pound."
After hearing noises outside his home at Retreat at Twin Lakes, John Good says he stepped outside and saw part of the encounter between the two and yelled at them.
"At first it was, 'What's going on?'" Good testified.
"No one answered and then at that point the person on the bottom I could finally see and I heard a help, and then at some point I said, 'Cut it out' and 'I'm calling 911' when I thought it was getting really serious."
Good testified the person on the bottom appeared to be Zimmerman, based on clothing and skin color. He added the person on top, straddling the neighborhood watch volunteer, was Trayvon Martin with his arms moving downward like a person throwing punches. He said the person on top was in something like a mixed martial arts position.
"It was the first thing that came to my mind, yes, that the person on top was ground and pounding the person on the bottom."
Good also testified Friday he thought it was Zimmerman who called out for help.
"Could you say unequivocally to this jury who was saying something?" prosecutor Bernie de la Rionda asked.
"One hundred percent? No," Good relied.
"And you believe the person on the bottom would have been saying something when they observed you?" de la Rionda asked.
"Correct, and if it was coming from on top, it would of echoed off a wall instead of coming directly at me," Good said.
However during his testimony Friday, Good also admitted he never say Martin slamming Zimmerman's head on the concrete, as Zimmerman claims.
Friday was the fifth day of testimony in the Zimmerman trial. It's expected to last another two to three weeks.
If convicted of second degree murder, Zimmerman could get life in prison.