Most of the time, parents love their kids. They just do. It might not feel that way when they take away your skateboard, or ground you, but you have to keep in mind that your parents are people, just like anyone else. They want what's best for you, and to a lot of parents, skateboarding is a bad influence and a dangerous thing for their kid to do, so they want you to do something else.
The best thing to do in this situation is to talk to them. Try to do it at a time when they aren't busy or upset, and when you aren't feeling angry or hurt.
Now, if you've been frustrated by your parents not supporting you, there's a good chance that you've done some yelling, and maybe some rebelling against their rules. Stuff like that does NOT help your cause! I know it's natural to want to yell - I get mad really easy myself - but you have to remember that your parents are responsible for guiding you into becoming a good adult. That's a lot of responsibility, and they're nervous and scared and frustrated too. And they are going to make mistakes. They're people. But getting angry and yelling and breaking stuff doesn't help you get what you really want.
And what do you really want? Well, you want your parents to be on your side, to support you, and to be proud of you! That's what everyone wants!
So here's a key - when they make rules that sound crazy, or too strict, your best bet is to go along with them, or to try and talk to them and explain your side. But in the end, it's best for you to pick your battles, and not to fight on the minor stuff. If your parents are against skateboarding, but they let you skate as long as you wear a helmet, then be thankful that they are letting you skate at all, and wear that helmet! If they don't want you hanging around with certain other kids, then maybe you need to find new friends. It might not look like it, but your parents are trying their best, and they think they are doing what's best for you.
If your parents are against you skating at all, then you have a harder road ahead. But screaming and fighting isn't the way to win. Submission and displaying good character are better. But in the end, if your parents command you not to skate, then you are going to have a hard time getting them on your side.
If your parents go beyond this, to breaking your skateboard, or hitting you or hurting you in any way, then you should talk to a counselor at school, a pastor at your church, or someone like that.
But otherwise, the only thing you can do to win your parents over, in the end, is to talk with them calmly, and to obey them and hope that they soften up. You could of course just go against what they say, and rebel, but in the long run this is a bad idea and you will regret it. I know that here on a skateboarding site, you might have been hoping for me to say you should rebel and fight your parents, but here's the thing - if you have parents who are making rules, then you have parents who love you. And that's valuable. I know it might not feel like it right now, but if you had parents who didn't care what you did, you would be in much worse shape, especially when you grow up. Be thankful that your parents care, and talk to them about how their rules make you feel, and if there's any way you can change their minds. Just talk to them, and listen to what they have to say. But in the end, for your own good, you should respect them.