NC's as about to out myself 
First, your DS is cool, the other boys are bullies and won't amount to much. Remind him of that.
So, I play roller derby. High level, I play for the top team in the world east division and I used to play for a very high ranked team in the states.
I play a fast, aggressive, full contact sport. Though it is predominantly a woman's sport, men's derby is fast growing. There are junior leagues all over the country, if you thought he'd be interested I could help put you in touch or recommend a local league?
I play with a lot of men - mainly in support roles (referees etc), and the level of skating is incredible. I work with a lot of ex-speed skaters, who are almost all male, and the fitness and hardcore aspect is amazing.
Roller skating, like skateboarding, BMX, snowboarding etc is an extreme sport. It's very cool. I'm guessing the bullies know this, they are jealous and wish they were as cool as your kid. This is easy for us to say and believe, because it's true, but not so easy for him so remind him.
The skill your DS has is probably already great, judging by your post, but if he keeps practising he can play high level, and believe me, he'll not give two shits about he bullies then. Not when you are being paid to skate, when you are being taken to parties and treated like a hero. When people ask you to sign their helmet because they admire your skill. When kids make banners when they come to watch you.
It's all worth it - all the teasing and sly digs will fade, but the feeling, the pure adrenaline rush, the admiration, the enjoyment and the euphoria, that will only get more and more.
Make sure he doesn't give up. Your kid sounds awesome.
(Oh, and YWNBU)