Standing up for a domestic violence perpetrator is not the hill I am going to die on, and standing up for rich NFL players is not the most important labor rights cause you can devote yourself to. Still, NFL players are labor, and policies about dealing with labor should be clear, contractual, honest, and not arbitrary. I'm uncomfortable generally with punishing employees for things they do off the clock. I get that major league sports players are part celebrity - and that for better or for worse 'image' is at least a minor consideration when they're being hired - but hiring decisions of individual teams are different than random sanctions imposed by the league.
The NFL does punish players for things they do off the clock, and to the extent that they do, a domestic violence perpetrator is certainly high on the list of people who should be punished. But any employee deserves some sort of due process, not a make it up as we go along in order to cover our asses process.