Negligible. Coaches will yell at you. Fans will yell at you. Owners will yell at you and cut your pay. Ed Hochuli will call you for holding even though you didn't do it, and the league will yell at you if you argue with him. Essentially, you are giving your body and your current and future health to your employer so they can hopefully average 4.7 yards per rushing play instead of 4.5.