It would appear that some men and boys enjoy violence recreationally.
Football violence is often well planned, organised and it appears, enjoyed as a manifestation of a warrior identity.
In fact, the actual football match is just a 'carrier' for pre-planned violence between two or more warring groups.
The violence isn't subtle - It's us v. them, full stop. No deep thought required, no weighing up the rights and wrongs, just 'Get them!'
Merely wearing the wrong colour scarf may be, and has been, a death sentence, even if the wearer is just quietly walking down a street at some distance from the stadium. He's the other side. He's not us. Get him!
If you look at footage of recent 'disturbances', it's almost all, if not all, men and boy-children taking part - very young children are often in the thick of the most dangerous and violent confrontations.
Just as football violence is based around football, but isn't really about football, any number of things may trigger recreational violence, possibly actual emotional responses to something terrible like a murder - though only some murders - or some inaccurate rumour spread on social media.
Whatever the reason, they quickly turn out - the boys, some of them little boys, with their masks and their ready supply of missiles and Molotov cocktails.
It's almost as if they were just waiting for the opportunity to go out and have some 'aggro'.
The target of their violence varies, mostly people who are in some way not like them, or the police who are trying to protect the people who are not like them.
Over time, that may change from people of a different religion, to people of a different race - different victims, same violence.
During the trials of people involved in serious rioting in Dublin, a frequent defence was that the rioter 'just got caught up in the moment' and torched a bus or a police car or smashed a shop window and treated themselves to some designer footwear because everybody else was doing it.
It was the opportunity for extreme violence that triggered them, not why it was happening.
Some women join in, but usually it is men, youths and, worryingly, very young boy children, and often looks like it is a game for them.
I assume it's due to cultural and social conditioning about violence being a validation of 'proper' masculinity?