OO Design for my new PvP styled arena plugin.

I'm currently working on a new plugin. It's just a PvP plugin, but before I start doing too much programming,
I want to make sure I've got the right design. That's why I'm asking here.

The reason I am making this plugin is to use it again later, should I want to make another arena-themed plugin. It should be programmed in a clean, OO designed way.

Would you mind checking it out, giving me some tips? I have a few questions about my design/code:

• Do you have any suggestions?
• Things I should do another way?
• Things that might make life easier for me?

https://github.com/WorldofWoutCraft/WoWPvP

If you feel like helping, feel free to create a pull request