Mule tried to attack me?

There is a mule stallion were I keep my horses. Yesterday when i tried to move him, he was trying to bite at me,pinned his ears back and wouldn't stop pushing on the gate I was trying to open. Then i made the mistake of just putting a lead around his neck to put him in a different stall and he dragged me down the barn and I scd up my arm pretty good. I've never delt with such an angry animal before, usually he is really friendly. My question is, what do I do in that same situation next time? The hardest thing was opening and closing the gate while he was threatening me and leaning on it. I was really nervous about getting bit. Should I smack him? Should I ignore him? What should I do!? thanks