The cops were not going to beat Andor, or kill him.
There was no immediate threat.
Self defense requires an immediate threat.
They wanted to impound his ship, because they probably get a kick back or a bonus for doing that. They targeted Andor because he laughed at them, and this was their revenge, a legal quagmire and a financial sink hole.
To impound Andor's ship, they needed to take Andor downtown for questioning, and then eventually see him suffer through a day in court, where they can "legally" take his ship, and send him to jail for years, although they didn't know that the ship was stolen, so they couldn't have impounded it anyway. The ship would have been returned to it's legal owner, and Andor would have been sold into slavery.