Database scheme - help needed

I have been working trying to work out an scheme of a result database for my track and field club. As I am relatively new to MySQL and PHP, I would like to know from you, if you can give me any tips how I can improve the attached database model.

Thanks a lot!

The newest model can be seen here:

http://www.faramelli.com/php/database.png

http://www.dreamhost.com/rewards.cgi?faragerri