Pushing kids to do extracurricular activities often makes them hate those activities.
If he loves skateboarding and scootering, encourage him in those, but don't force him. They are great excercise, valid hobbies, and skateboarding has actually become a recognized sport.
Limit his TV, computer, and video game time. Then he'll be forced to do something good for him, like reading or going out to play.
When he decides to go for a sport, or gets into skateboard competitions, or whatever, make the rule be that if he gets in too much trouble, you'll take him out of the sport. This makes the sport a reward, and he'll fight for it. It also improves behavior around the house. :)
Trust me, my son used to do nothing but play video games. Now, he's in basketball, football, track, student council, and physics club. I always threaten to take him out of stuff if he misbehaves (though really, I LOVE that he's doing all this!)and he will do almost anything to avoid giving up his "play time".