A good mate of mine had his football 'career' ended on a Sunday league pitch in the team I played in with him, with a knee height two-footed challenge snapping his bone in half and puncturing the skin and sticking right out of his leg. It was a vengeful tackle on the halfway line in time added on after the 90. Was on crutches for two years, but thankfully wasn't a self-employed manual labourer, nor did he have a family at the time. Incidentally, Labour were in power at the time.
Also during Labour's reign of terror

we also had a game shortly before that where a team we beat jumped on and attacked the referee immediately after the game. They were biting and punching, and we had to get him free and escort him by car away from the pitch. They were banned for life from playing Sunday league. I gave up Sunday League shortly after all that. Why give up your Sundays to witness thuggery you'd be shocked to witness on a Saturday night in the dodgiest pub in town?
Also, in a non-Sunday league game, with an organised, refereed Tuesday night 5-a-side league I play in, two kids refused to get off the pitch, cycling their bikes around the centre circle etc. One of my teammates eventually just went and grabbed one of the kids and started leading him off the pitch, and about 10 of his older mates came out from nowhere and swarmed the pitch with bottles etc. Our teammate got stabbed in the leg with a screwdriver amongst all that, and bottles were being smashed and wielded by these guys. It went to court and the attacker got prosecuted.
The Sunday League stuff was in Battersea, and the 5-a-side was in Islington. Obviously that latter one wasn't really football-related - just some guys blatantly looking for a fight. But still, some serious thugs out there.