most of the time, it's because you have them cornered.if they have an escape route, they will take it.(I say most of the time).only really had one big boar charge at me,that was because of a couple puppies I had with me and they ran between my legs and behind me,the hog was charging the dogs and I was in the way.I shot him at 4 ' with shotgun.
If you have then bayed with dogs, then don't get in there way.other than that, shoot them and wait till they bleed out and you should be fine.

just always be careful whne dealing with game animals of any kind.