The reasons for violence at soccer have nothing to do with 'boredom'.

The supporters in the stands understand the game inside and out, often better than some of the managers of the teams they support. They play the game themselves at various levels, and are passionate about the sport. They could no more be 'bored' by it than anyone else could be bored by their passion. That's the first time I've heard that particular theory, but it's nonsensical. You don't see fishermen throwing down their rod in a fit of boredom and smacking a passer by in the chops because there was a lull in the catching of fish.

If you want to understand the real reasons, rather than a lazy theory from someone who likely doesn't follow soccer and who likely personally thinks its boring, then I shall explain.

Tribalism is one of the primary reasons for violence. Tribalism isn't simply a nation v nation thing, it's a city vs city thing. And in many cases this tribalism is at its worst when there are two pro clubs in the same city. I'll give you Celtic vs Rangers. Two clubs from the same city, one club created in the 19th Century for Catholics, one club created for Protestants. The rivalry goes beyond mere sport, and is pure sectarian bigotry. Regardless of whether there happens to be the most exciting game ever played going on right in front of them, one group is screaming 'Derry's Walls' and the other is howling 'Bobby Sands' like werewolves at a full moon. Both clubs have deep and long connections with terrorist groups, and murder has been done in the name of which group of sociopathic religious nuts is the more correct in their slightly different forms of worshipping the same god.

Political affiliation is also a motivator in the violence. European soccer is a major source of young, impressionable young guy who can be recruited into the ranks of (largely) Fascist and Anti-Fascist groups. The Ultras have branches in many major European clubs, if you see a section of the ground with huge national or regional flags being flown, or flares being set off, or possibly Fascist salutes in evidence, then that's likely where the Ultras are congregating. Obvioulsy no-one needs a kicking more than a Fascist, and so often you'll see anti-fascist groups piling in and breaking heads.

Casuals. The Casual movement is the reason soccer violence came to global prominence. Young, well-off young lads, with an eye for fashion, a love of soccer, and the need to smash other young lads' heads into putty, the Casual movement grew out of the London, Manchester and Liverpool youth cultures, and transferred itself to the soccer terrace. These groups were often organized to the point that they carried business cards and had a genuine heirarchy, complete with youth groups for under 16/18 year old members. These groups might be called the Under 5s, or The Tufty Club, or some other tongue in cheek reference portraying the younger members as infants. The Casuals generally only fought other Casuals, though a couple of somewhat horrendous incidents did lead to large numbers of deaths, including Heysel, where 39 people died and 600 were injured. There was also the tragedy at Hillsborough, leading to 96 deaths and around 800 injured.

Eventually the sluggish monolith that is the police authorities finally caught up with youth movements, and a number of measures reduced the violence to somewhat manageable levels. Though police/governmental incompetence and Casual violence did create a perfect storm of tragedy in the shape of Hillsborough, leading to 96 deaths and around 800 injuries.

To say the violence in soccer is created by boredom, though, that sounds a lot like someone who isn't a soccer fan.

If inherent boredom was a genuine reason for violence then cricket matches would routinely erupt into frenzied bloodbaths, and baseball games would be likewise.

I couldn't even imagine what sort of murderous savagery would occur at the World Chess Championships.

I would discontinue reading whatever publication you read that particular that theory