So let's be clear - he works full time, so doesn't have that much to do with the kids during the week -
And then basically demands a day off to do what he wants (yeah, it's sport, he's not playing it for 7 hours, is he? I go for a run, it keeps me fit, it takes an HOUR.) So he's available as a family dad for one day a week?
Yes, it's selfish. No the OP is not being U.
I am hooting with laughter at the suggestions that OP take the kids to see him play, so they can hang out together. Get real. He's not going to agree to that. If he wanted to be spending time with his kids, he'd be arranging his life to fit them in round his matches already.
The reality is that when you have children, YOU HAVE TO COMPROMISE. You can't just please yourself. If it is sport that is important to him - fine, he can find something less time consuming that keeps him fit. If it is the social side, then can't he meet them for less time, somewhere else in the week? Children's needs change over time - it is possible he is looking at his sport taking a back seat for a few years, and he can then take it up again. A bit like I am.
The op h said she does a sport, but doesn't insist on doing it when it is inconvenient for the family. Unlike her DP. Who doesn't want to let his team down - but seems happy to let his partner and children down. What selfish entitled behaviour.