underdog

A competitor thought unlikely to win.

They were the underdogs in the basketball competition.

In Athens, the Americans are underdogs to the Chinese and the Canadians (the Canadians!)

Somebody at a disadvantage.

Laszlo: Isn't it strange that you always happened to be fighting on the side of the underdog? Rick: Yes. I found that a very expensive hobby, too. But then I never was much of a businessman.

A high swing wherein the person pushing the swing runs beneath the swing while the person being pushed is at the forward limit of the arc.