not have a leg to stand on 无法证实；无法解释（理由）；站不住脚；有口难辩

【例句】
Without written evidence, we don’t have a leg to stand on.
我们没有书面证据就站不住脚。

The man with a gun and $ 300 in his pocket was accused of robbing an oil station. He did not have a leg to stand on.
这人身带一支枪，口袋里有300美元钱，被人指控抢劫加油站，他真是有口难辩。