A player in my campaign wants to outfit his character with roller blades. He thinks that it would be a specialization within other skills to use them.... gymnastics to do fancy jumps, running to go faster than normal etc.
I was thinking it should be a specific skill for each mode.. skates (roller or blades) and skateboards.

Those should be a specialization of the normal athletci skills. I doubt roller-blades are going to play a starring role in your game, so they should not be broken up into a seperate skill.

I'm with Bob on this one.

Now, rocket-powered rollerblades, otoh...

Depending on how often they're going to come up, I'd either go with Athletics, or let them count as a knowledge/hobby skill. If he wants to use them as a dodge bonus, then Gymnastics is definitely the way to go; if he wants them to increase his getaway speed, then try athletics. But if he just wants them as background color for his character, and isn't going to use the skill in combat, then give it to him at the knowledge skill price. Even if they come up once in a great while, they're not going to unbalance anything.

i would just put it under the normal skills.

You want speed, use run

You want tricks use gymnastics (how many runners are actually going to in the gymnastics sport, it must mean more than that)

Edward

I've actually made a new skill for a new item:

Pilot: Hoverskates

Hoverskates are a brand new item to take the "YT Smartwheels" from Snow Crash to a new level. After playing Jetset Radio Future for about three days straight, I decided I wanted to have a hover-skating NPC in the game, a tag-messenger of sorts. Hoverskates use highly concentrated repulsion fields to lift the wearer a few inches off the ground, and wearers can use that repulsion to attain velocities like rollerblades, or faster.

But remember: You can't go over water unless you've got POW-ARRRR!

I was thinking of a similar idea with skate boards ala back to the future.
Hover boards that only work over solid objects, using a limited magnetic repulsion feild.

...consensus already reached in a previous thread on this topic.

Athletics (Gymnastics and/or Running)