NFL legend Bruce Smith says he was FURIOUS when he saw the footage of a youth football coach punching a 9-year-old player ... because Smith endured similar abuse as a kid.
"This was disturbing," the 57-year-old Hall of Famer tells us ... "In my opinion, it was an assault and it made me reflect back when I was attacked and dragged around a baseball field by a baseball coach as a young kid."
Smith is obviously referring to the incident in Florida -- in which former law enforcement employee Gerrel Williams belts one of his young players multiple times during a game.