I would imagine this depends a lot on age and history (e.g. a horse that just started biting versus one that has a pattern). But I don't know anything about horses; do those details matter? Should they be in the question?

@Monica No, they don't. Being bitten by a horse is so very painful that it's not something that would be tolerated very long

Often the why is important to determine the best way to respond. Unfortunately it's usually because people let them get away with it. I worked with one pony who came to the rescue because it had severely bitten a child's shoulder. Turns out the parents had been hand feeding and letting it get away with all kinds of bad behavior "because it's so sweet and would never really hurt anyone."

On the other hand, I also worked with a former "trail ride" horse who would get a saddle jerked on in the morning and wear it all day. It took three weeks before he calmed down enough to let a saddle blanket sit on his back while I groomed him. Amusingly, he had no issues being ridden bareback, but he was all teeth if you walked past with a saddle.