It is slang for being very badly defeated, usually in some sort of physical struggle. "Tom got into a fight with somebody in the bar and got his butt handed to him." "When the Americans invaded Canada in the War of 1812, they had their butts handed to them."

When you threaten somebody, your plan is to kick their ass. If you beat them, you can say "I owned his ass!" For handing someone their ass, the idea is this: not only do you own their ass (as in "possess" it), but the person suffers the indignity of having to receive something that is already theirs. As my colleagues have pointed out, it indicates a sorry defeat. And here's a cartoon: www.angryflower.com/realas.html

首先，谢谢你回答我的问题。很有用！一般来说，“get one's ass handed to sb."是“被人痛打了一顿“的意思。可是，sometimes we also apply the phrase to any other activity in which you can "lose big time." Example sentences: "He got his ass handed to him when he played golf with Tigard Woods." (meaning: "He lost really bad when he played golf with Tigard Woods.") 另外一个例子：“When he opened up his own burger restaurant and tried to compete with McDonald's, he lost tons of money. He really got his ass handed to him." (意思是：“when he opened his own burger restaurant and tried to compete with McDonald's, he lost a lot of money. McDonald's did much better business than he did."

You need to give us the full sentence, but if someone is getting their ass handed to somebody, then it is slang for someone who is owned by someone else.