Simple. Many people find the spectacle of competition entertaining.
The problem is that top athletes and so on are quite possibly starting to reach the limits of human performance and so the differences in what they can achieve is narrowing further and further.
As for football hooligans, they are not fans. They are quite simply trouble causers - they view the sport as something almost tribal and will use any outcome as an excuse to incite violence. In short, they're a*seholes.
