It's a stereotype, maybe even a generalization. It's not "very true". It can't be; there's about 130,000 men in the world who play soccer professionally or semi-professionally.
Just because certain cultures incentivize hooligan behavior (looking at you, London), doesn't mean all everywhere do.
I think it's because of the size difference in the fan base. Nobody in the USA, for instance, gets in fights because of futbol, but football rivalries have caused death. Heck, one of my coworkers saw a man get castrated because of a college rivalry on game day. The difference? Fan base in USA is very small for futbol, very large for football. A larger fanbase means that the long tail of the distribution curve is more likely to pop up.
I remember the average professional soccer player loses ~10 points of IQ per decade due to the repeated impacts to the head. There was a guy advocating for the introduction of helmets in children's leagues because of the potential.