Ex-NFL RB Zac Stacy Brutalizes Ex-GF in Front of 5-Month-Old Son, Terrifying Video

Former NFL running back Zac Stacy brutally attacked the mother of his child, punching her in the head before slamming her into a television as their 5-month-old son sat feet away ... and the terrifying incident was captured on video.

TMZ Sports has learned ... the disturbing altercation happened at 30-year-old Stacy's ex-girlfriend's home in Florida on Saturday.

We're told Stacy became furious and aggressive with his ex during an argument ... and that's when video shows the former 5th-round pick swinging at her head before yanking her off a couch, tossing her across the room and into the TV.

The TV then falls on top of the woman as she tries to calm Stacy down ... but he throws an object at her and storms into a corner.

Throughout the video, you can hear the woman begging Stacy to stop.

We're told the woman called cops immediately after the altercation, but Stacy fled the scene before law enforcement was able to arrive.

We're also told the woman filed for a restraining order Monday -- for her and her son. In those docs, Stacy's ex claims the football player came over to her house around 2 PM on Saturday ... to see his son.

While there, she claims he flew into a jealous, violent rage.

"He punched me several times in the head! I begged him to stop because the baby was on the couch just a few feet from where he punched me," the woman wrote in the restraining order application.

She continued ... "He then picked me up and threw me into my TV. The TV began to fall and he turned to make sure I wasn't getting up. As I laid on the floor he began to yell at me, telling me I'm destructive. He then picked me up off the floor and off my feet and body slammed me into our son's bouncy seat."

That's when she says Stacy said "I love you" to their baby boy, and bolted. In the restraining order docs, the woman adds, "I fear for my life and my children's lives."

She says she went to the hospital, where she was treated for a possible head wound, as well as bumps and bruises.

Stacy was drafted out of Vanderbilt by St. Louis in 2013 ... and played 2 seasons for the Rams. He joined the New York Jets in 2015 ... and has been out of the league ever since.