The fight took place around 3 p.m. Thursday at the franchise on Flatbush Avenue Extension in Downtown Brooklyn.
Teenage girls can be seen on the video punching and pulling each other's hair and rolling around on the floor for several minutes, while the man capturing the brawl on video narrates.
"I'm in pain. Serious bad pain. My body hurts. My eyes hurt," victim Elizabeth Ballinger said.
A man can be seen stepping into the fray trying to break it up.
"Back up. Do not fight," the man says.
That's followed by some back and forth shoving, and the man appears to throw a punch, at which point the crowd turns on him and he is mobbed by teens throwing punches.
Caution: Graphic content including language and violence
Another woman can be seen beating a girl on the floor of the McDonald's.
The man runs out of the McDonald's and the video's narrator can be heard shouting: "Kill him! Why're you not killing him? Y'all gotta kill that old n----! Y'all gotta kill him! Kill him! Kill him! Kill him right now! Kill him right now! Kill him!"
The man who stepped in, Iver Whittingham, spoke exclusively with CBS2's Ilana Gold.
"I have never been beaten like that in my entire life. It's a tragedy," he said.
After a trip to the hospital and a giant knot on his head, he said he didn't regret getting involved.
"I have a daughter and I think if something like that happened I would hope someone would do that for my daughter," Whittingham said.
Ballinger said she knows the perpetrator, but wouldn't say what prompted the melee. Police sources said they have the 16-year-old in custody.
"I was thinking why is she attacking me? Why is she hitting me? I blacked out," she said.
Ballinger and her family couldn't be more grateful that Whittingham tried to help.
"He's a hero. He's gotta get a good Samaritan award for that," Ballinger's father said.
Another McDonald's Fight Goes Viral
"It's a sin. It's a shame," a regular customer named Frank told 1010 WINS' Glenn Schuck. "That's our society. It's all over the country you see that. Again, the upbringing, no conscience whatsoever. This country, I hate to say it, with these young kids today, is going down. It's a sin."
There's usually a security guard at the McDonald's at all times, but it's not clear where that person was Thursday, Schuck reported.
Police said they are looking for the teen behind the camera who even recorded himself during the brawl.
Investigators said they are also searching for three others involved in Whittingham's attack.
"Something needs to change, some way, somehow we need to fix this," he said.
It's especially concerning since another vicious fight with a group of teens happened in March at a different Brooklyn McDonalds. Six of them were arrested.
"I hope they can learn from this. I just pray they change and realize what they're doing," Whittingham said.
The victims just want the violence to stop.
Security has been stepped up following the fight. There was also a shooting at the location a few weeks ago.
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