Has he talked to both teachers and the guidance office? One thing that may factor is the rest of his schedule - sometimes the only open slot in a class means he can't take several other classes. When I was moved out of and back into of GT classes in 7th grade, I had to leave the art teacher I loved for one I hated because the first teacher's 4th period class was full. I was so sad about that, and later she admitted she wished she had pushed for one more kid in that class (me). I was also not able to stay in the same gym or geography classes.
I did take Ecology vs Pre-cal my senior year because of the stress of two college-level courses I was taking at the time. They were offered at the same period so no other swapping necessary. I had an otherwise full courseload. I had to plead my case with both my mother and the guidance office. The teacher felt that I was doing fine with a solid B at that point but I honestly didn't want another math, knowing I was planning on majoring in a non-math related field in college. I only got through Algebra II with some serious tutoring at the end (after I'd signed up for PreCal for the next year). That was the main reason my mother approved me dropping it.
Has the year started yet or is he worried about the *perceived* workload? How did he find out it's hard? And how long would he have to switch if it's really that hard?
Another thing to think about is the other 3 years. My SD kept a class she didn't like in part because changing would mean that later she wouldn't have the option to take a prerequisite for a specific class only offered to seniors. So he should look ahead to see where this might impact him later, if the schedule means he won't have room for something that really interests him.
IMO, I'd make him at least try the class, and withdraw if he really needs to. But he hasn't even had the class yet, has he?
So, basically, if he switches, make sure there isn't some other impact you haven't yet thought about.
RE: football, my SS played football and wrestled all through HS and took AP and honors classes. While we did encourage him to join a team, it was made very clear that we expected much more than the school-required 2.0 to continue to play. Your son needs to balance sports and school and if sports makes school suffer, then he should reconsider playing. My SS ended up tutoring many of his classmates and I think MAYBE one got a sports scholarship, while he got nearly a full academic scholarship to college. It was tough, yes. I also wanted to point out to some people that not all schools are on a semester system. Many still do a full year of 7 or 8 classes, so if he's taking a lighter load, it may not be just for fall.