Is it bad to play Tug-o-War with a pit bull mix?

Me and my wife just adopted a 10 month old Pit bull-Labrador mix he is 60-ish Lbs and I was curious if me playing tug-o-war with him would reinforce bad/aggressive behavior. He is a very sweet and loving dog but when we take him for walks he gets uneasy and protective of us if it is dark and a stranger gets too close. I just want tips on ways I can play with him and tire him out without making him too aggressive.