[Eric Bareiss]

I don't know if you guys looked at this:

<R13>
In no case, will traction devices that damage the carpet or other playing surfaces be permitted. Traction devices may not have surface features such as metal, sandpaper, or hard plastic studs, cleats, or other attachments.

I know it doesn't say anything about glass or marbles but I think that would be up for interpretation. I would ask FIRST before I showed up to a competition like this.