I agree with "wuss."
I grew up in the countryside, and I know not to approach large (except that was a pretty small and skinny looking cow) animals without carrying a large stick. A sharp whack on the nose will send just about any large beast running.
But if you're charged (and unless it's a bull, that's usually that's just curiosity, not aggression) and you don't have a stick, standing your ground and delivering a kick on the nose is almost as good (but more likely to go wrong). Running is a bad idea and will just make it more excited - again, unless it's a bull, when the idea is to get out its way as quickly as possible.