Nothing wrong with following sports- so long as it doesn’t interfere with his obligations or take over his life. I myself am a big baseball fan, and I still follow a the team of my hometown despite having lived in E”Y for about 17 years (I endure quite a bit of teasing from my kids, and even my husband :-))
Other thing is, like cantoresq brought up, be careful he doesn’t conflate the game with the personal lives of the players. Also, I heard that soccer games in the U.K. can get a bit rowdy, so if your son wants to actually go to a game, consult your LOR.