These people are "reenacting" a battle between Moors and Christians. Valencia was in Muslim hands for about 200 years until it was conquered back by Christians in October 9th, 1238. To celebrate this, there are lots of festive events from 1st to 9th October, and the "battles" are a popular one. Apart from the obvious historical mistakes, such as cannons having not been invented at the time, or the fact that people from both "armies" were manning the cannon together, I love how some of them are wearing ear protectors over their costumes. Not accurate at all, but funny, entertaining and safe (at least for them, the rest of us will probably get deaf - we use powder in most celebrations, the noisier the better).
Love your narrative, anything to please a crowd