DTS2 had (as usual) an enormous tantrum after being told to come off Fortnite tonight - the rule is, he gets an hour to play and that's it - his behaviour is absolutely horrendous if he's on any longer. Tonight he was told he had an hour, left for the hour, no interruptions - I went back in after the hour and told him that was it. He asked for a couple of minutes to finish off a round and I said ok, then at the end of that it was clear he wasn't anywhere near finished and it was just a fib, so I switched the internet off. He had been told and told and told and told that he had strictly an hour, we were going out so there was no possibility of extra time, etc etc - and he still went apeshit 
When I say apeshit - shouting, screaming, swearing - picked up his belt and swung it at me and DTS1, we both got hit with the buckle (DTS1 worse than me). More tantrumming, more swearing, threats to call Childline, threats to leave home, and so on. Told me what an awful person and mum I am, he hates me, he'd rather just live with DP as DP doesn't restrict his Fortnite time... on and on and on.
I loathe the game, his behaviour is terrible after playing, he's bright red and screaming - I'd never have let the DTs have it myself but DP caved in when he learned that most of the kids at their football club play (same age - all 8/ 9/ 10yo) and quite a lot of their school friends too. DTS1 will whine and whine for more playing time but doesn't have an absolute meltdown over it like DTS2.
He's slightly calmer now and I said I'm not going to discuss it with him again, he can wait and talk to DP when he gets back from work as he clearly won't listen to me anyway. I've switched the internet off to his PC and frankly it won't be coming back on any time soon, his behaviour has been appalling and he needs to understand that - but I'm at a loss for what else to do, he doesn't even seem to get that he could have seriously injured me and/ or his brother.
A close friend's DS turned violent at 13/ 14, they'd been very close up to him turning around 12 and then suddenly he started being rude, secretive, school refusing etc - it ended up with him hitting her, threatening her etc until she had to arrange for him to live with his DF as she was scared of being injured. I keep thinking about that now and thinking, what if that's DTS2? What if he starts doing that when he's bigger than me and stronger than me?
If anyone has any words of wisdom they would be much appreciated. I'm still in shock really and upset that he's spoilt what had been a nice day (we were going to go to his sports club too but couldn't as he was being so awful) and maybe I'm catastrophising based on my friend? But really I just don't know how to make him see that his behaviour is not normal/ acceptable!