I would suggest short term activities, with alternating between sports and more art related activities. Any session that is started must be finished, not only because others may depend on him, but completing any task is a lesson in itself.
With DD and DS, only the swimming lessons were mandatory. Luckily, they both enjoyed it.
They had pre-school activities such as dancing, painting, arts and crafts.
They tried karate (because Power Rangers) for 2 sessions.
They played ringette and hockey for 3 years.
DD participated in the annual school play, both as actress/dancer and making decorations.
DS did some mountain biking for a while.
Both of them are still enjoying different sporting activities now that they're adults.
Some children will like to do an activity but not necessarily be competitive at it and that is alright too.
I was never a competitive person when it came to sports. I was about 8 or 9 and I wanted to learn to skate properly. I was not accepted because I was not good enough (duh!). That kind of turned me off for sports in general. I finally leaned when I took an adult class with other non-sporting people. However, I spent several years in choir / singing lessons and enjoyed it, even if I was never more than passable at it. The choir director always made everyone feel included and I'm sure a couple of kids discovered talents in themselves thanks to him.
Edit: Cut and paste is not my friend.