Legal Question in Criminal Law in California

Yes, your character would be defamed in such a circumstance, but because the deposition is considered a court proceeding, however scurrilous and malicious and hurtful the lies may be, the liars that tell them at depositions are immune from lawsuits.

Can someone do this? Yes. Is it actionable as defamation? No.

Statements made during the course of a lawsuit -- including those made by a witness in a deposition -- are privileged and cannot support a judgment for defamation. But if the witness lied about a material issue while under oath, he can be prosecuted for perjury.