I missed your parenthetical. That makes more sense.

FWIW, I tend to agree with parents who tell their kids they don't get to choose to be idle. I'd let a kid skip fall sports only if they had plans for winter and spring sports.

The age of your kid matters a lot. Under 12 I'd just make a kid play soccer because they have to run a lot. Over 12 I'd make him run cross country or discover how to weight lift at the gym and mix in cardio. Those both fall into the category of teaching a kid workout skills that will carry into adulthood.