I have learned to approach from the rear. Once there and having poked it in the haunch with a stick, i move around to the head and poke the eye, ...cautiously and with loaded gun handy. So far so good...
Don't know what I'd do if one jumped up and came at me..hopefully the right thing.
I sometimes have a pistol with me when I hunt and when that is the case it makes things a little easier since I have a free hand.