Explain to him that unfortunately his struggle to lock the door has resulted in the damage, and that you are sorry to have to ask him to cover the cost.
If he is awkward about it, put it in writing, with a copy to the Company Manager of the company producing the panto. Theatre companies rely heavily on the people who provide digs - and may tell him to behave himself. though i doubt there would be any legal redress through them. But he won't like his professional reputation sullied!