The first rule of Rumblr is, well, it doesn't matter because Rumblr is a hoax. A few days ago, Rumblr, the self-described "Tinder for fighting" application, was announced. Then came news that it was a marketing ploy for a new public relations firm. Still, that leaves the question, would fighting by matchmaking or a real-life Fight Club be illegal New York?
The short answer is that even if two people fight by agreement, which is called "combat by mutual agreement" under New York State Law, the combatants are not immune from criminal laws like assault and criminal possession of a weapon. If two people agreed to fight in a fight club or via a fighting-matchmaking app and then fought, they would be committing assault. The degree of assault would depend on the nature of the injuries sustained and there could be weapons possession charges if any weapons were involved.
That's right, if two people agreed to fight both combatants could be arrested in what is known as a cross-complaint, where each person is a victim/complaining witness in one criminal complaint and a defendant in another criminal complaint. Cross-complaint type of arrests are not uncommon in New York, though the combatants unlikely meet via an app or in the basement of a seedy bar.
The phrase combat by mutual agreement comes from New York's law governing justification, also known as self-defense. That is, if parties agree to fight, one cannot later claim, hey, I was only defending myself. And, there is precedent for such claims. In 2003, Richard Rollins (who is also known as Boo) was convicted of manslaughter for shooting and killing a man his nephew had agreed to fight. Even though the man who was killed first aimed a gun at Rollins, an appeals court ruled that Rollins could not claim self-defense because the fight was combat by mutual agreement.
So, Rumblr or no Rumblr, Fight Club or no Fight Club, combat by mutual agreement is a bad idea. Though unlike Rumblr, which sought out publicity, the first two rules of Fight Club are: You do not talk about Fight Club.