From Longman Dictionary of Contemporary Englishnot have a leg to stand onnot have a leg to stand oninformalPROVE to be in a situation where you cannot prove or legally support what you say If you didn’t sign a contract, you won’t have a leg to stand on. → leg
Examples from the Corpus
not have a leg to stand on• If you didn't sign a contract, you won't have a leg to stand on. 