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.