In many states, such as Tennessee, fight club fighters can also be charged with participating in unregulated prize fighting. Because they are inherently dangerous, states put regulations around sports like boxing (and ultimate fighting). Organizing or participating in fighting events outside of these regulations is often a crime.

Note that amateur “fight clubs” are likely to be illegal in Texas, as it is almost inevitable that someone will sustain serious injuries. As a fight club’s events are not sanctioned professional fights, this would make this form of mutual combat illegal.

The answer is that, for the most part, they're not illegal. Consenting adults who feel like fighting in a private place don't generally break any laws. And most states don't consider it boxing, so long as none of the fighters are paid [source: AP ].