Why not threaten to cut Goodell's salary each time a domestic violence act occurs by a member of the league? Pitch Goodell against the team owners and watch them improve this problem. If he knows his salary/livelihood is on the line he'll crack down on the owners to police her employees. If the owners know they'll have to contend with this or any future commissioner with this repercussion to deal with they'll keep each other in check. Only other option is to use a two strike rule. Punishment on the first offense, kicked out of the league on the second.