Witness: Zimmerman, Martin were in mixed-martial-arts-style fight

(CNN) -- A prosecution witness testified Friday in the George Zimmerman trial that he saw the former neighborhood watch captain and Trayvon Martin engaged in a mixed martial arts-style fight the night Martin was fatally shot.

Jonathan Good said he heard a faint noise coming from the back of his home in the Retreat at Twin Lakes on February 26, 2012. When he heard a louder noise, he went outside to investigate. He saw two men engaged in a "tussle" on the ground.

"It looked like a tussle. I could really only see one person, and I think I described it as possibly being some kind of dog attack, because there are a lot of dogs that walk in that back area. I could only see an object," said Good.

Good is the 17th witness called to the stand in the trial of Zimmerman, who is charged with second-degree murder for the fatal shooting of Martin in Sanford, Florida.

Zimmerman told police he followed the teenager because there had been some recent break-ins in the area. During the confrontation, Zimmerman claims he was forced to kill the 17-year-old in self-defense.

On the trial's fifth day, Good recounted being 15 to 20 feet away from the fight between Zimmerman and Martin. Although he couldn't make out the faces of the people on the ground, Good said he could make out the color of their clothes. In crucial testimony that buttresses the defense's argument, Good said the person on top of the fight was wearing a black top like the black hoodie sweatshirt Martin was wearing that night, and the person on the bottom was wearing red. Zimmerman was wearing a similar color that night.

Good said it seemed that the person on the bottom was yelling for help. Good said he saw the person on top "straddling" the person on the bottom, and the person on top was moving his hands in a downward striking motion that looked like what he called a "ground and pound," a term associated with MMA, or mixed-martial arts fighting.

"It looked like that position was a ground-and-pound-type position, but I couldn't tell 100% that there were actually fists hitting faces," said Good.

Defense attorney Mark O'Mara asked Good to define the term "ground and pound."

"It's usually when someone is on top in a mounted position, I believe, in the dominant position. But like I said, the person on the bottom is able to throw punches back, but I did not see any of that," said Good.

Good said he went outside and called out to Zimmerman and Martin to "cut it out," but after getting no response, he went back inside and called 911, and that's when he heard a gunshot.

"I just heard a shot right behind my house," Good said on the 911 call, which was played in the courtroom. "They are wrestling right in the back of my porch."

The operator asked, "You just heard one shot go off?"

"It was either that or a rock that hit the window," said Good.

Earlier Friday, prosecutors called Greg McKinney to the stand to testify about images caught on the neighborhood's CCTV -- closed-circuit security TV surveillance system -- the night of the shooting. McKinney works for the company that monitors the neighborhood's CCTV system.

The cameras were recording images from the interior of the neighborhood's clubhouse. One image shows a shadow passing by one of the windows, and another image taken from another camera shows a light flash through one of the windows. The timestamps, even though they were a few minutes off, may help confirm the timeline of the shooting.