Ex-NFL player Zac Stacy was arrested in Florida and is currently in jail ... just days after he savagely beat his ex-girlfriend in front of their 5-month-old son, TMZ Sports has learned.
We broke the story ... 30-year-old Stacy repeatedly punched Kristin Evans, the mother of his baby boy in the head multiple times before picking her up and throwing her into a television -- all while she begged him to stop and the baby cried.
When Stacy -- a 5th round draft pick out of Vanderbilt in 2013 -- finally stopped attacking, he fled the scene.