Ex-NFL linebacker Bill Romanowski tells TMZ Sports ... there are a handful of dirty plays from his NFL career he wishes he could take back -- like the time he SNAPPED A DUDE'S FINGER!!!

Bill -- one of the most ferocious defensive players of all time -- is out in NYC for the Super Bowl ... and says he still feels bad about the time he was in a pile with running back Dave Meggett, grabbed the guy's finger and "cracked it like a chicken bone."

"I heard it and felt it ... and then heard the scream at the bottom of the pile."

Still, Bill admits, "There are probably 5 plays I'd love to take back ... but I can't."