I would say that you should vocalize a few things to your mom so that it's clear to her about how much you enjoy scootering over playing other sports:
1. Make it clear that you do not like playing sports. As in VERY VERY clear. Don't do it in an angry way, but still be firm about the fact that you don't like other sports.
2. Tell her about your love of scootering and really try to get her to understand. If she doesn't get it then just keep with it and she'll hopefully eventually come around.
3. She might have some stereotypes she's putting on her image of you riding. Show her some of the truly great scootering videos, ex: Matt Mckeen's Philly Crew part, the old Micro videos, maybe some of the Proto DVD or maybe even just some R-whilly stuff to wow her? Then maybe she'll start seeing it in a different way.
4. Make her understand that it's not about fitting in for you and that it's not about socializing or whatever other reason she has for wanting you to play other sports. It's not about having a unique hobby to look cool either. It's about doing something you love.
Boom.