Came up with it while playing Battlefield 1942. This is a person who changes to the team with the most/all of the captured flags points rather than helping his own team take them back.
That no-talent team-jumper just went to the other side instead of helping us out!
A hardo is a person who tries extremely hard at everything. Most times a hardo will try very hard at things that do not require excessive effort. For example, sports practices, gym class, etc.
Wow did you see Jack at practice today? What a hardo!