The issue of legality regarding fights is one that can be disputed, largely due to the fact there will be variations in what constitutes illegal fights. Generally speaking, any fight that is not sanctioned by the proper sporting authorities, which will be the case with boxing matches and mixed martial arts fighting events, can be considered to be under the banner of illegal fights. However, there are certain exceptions in place.
For example, in the United States there will be states that have laws strictly prohibiting fights, unless in is done in self-defense. Conversely, other states do not necessarily have legislation in place that specifically define illegal fights as punishable by law.
However, it can be deemed that all fights that occur outside the realm of sport and self defense to be considered as illegal fights. The main way to distinguish among the two is the fact that illegal fights are completely avoidable.
The issue of illegal fights will usually rise when a scenario of individuals fighting in a bar atmosphere. Because it can be said that the fight could have been avoided, it is considered not to be self defense. However, there is usually debate as to the interpretation of the fight, thus making illegal fights hard to properly define in certain situations.
Another important aspect to consider is that the concept of illegal fights does not only apply to people, but is also extended to include other species, particularly dogs. Dog fighting are considered to be illegal fights in the United States, with all 50 states having laws strictly prohibiting the practice. Dog fighting is considered to be inhumane and cruel treatment to these dogs, and thus, is warranted as a punishable offense by law.