The national sport of Thailand is Muay Thai boxing. It can be relatively expensive to see in Bangkok at around 1000Tbh for a ring side seat, attending elsewhere such as Chiang Mai will get you a similar seat for 400Tbh. There is more to it than one-on-one battles with Thai men kicking the crap out of each other.
There is typically 2 fight nights a week in Chiang Mai. One at Moon Muang Beer Bar Center and one at the Loi Kroh Beer Bar Center. You usually get 2-3 male Thai fights, an international competition (a foreigner (or farang in Thai) Vs a Thai), a female fight, and a special fight on the end.
Traditional thai music is played during the battles (see video to hear some in the background) accompanied by the soundtrack of trainers shouting instructions to their respective boxer. The fights are held in a ring in the centre of a crowd and surrounded by bars where waitresses will bring your supplies of peanuts and beer to you as you watch the fight. During the break you may be lucky enough to see dancing at the transsexual bars too.
It is well worth visiting the spectacle even if you are not into boxing, it is part of the male Thai culture and a key part of a lot of Thai fitness and life. Plus with the special events you may end up watching a stupid treat such as blindfolded 4 man boxing match, watch out referee!