OK, I work as a hunting guide and have hunted both mountain lions and boars (quite enormous ones) with a knife, with and without dogs. It isn't easy and it takes some practice, but it is an adrenaline rush like no other on earth.
However, throwing a knife at a charging boar seems like a VERY, VERY bad idea. Even if you somehow manage to stick the knife in him it won't stop his charge and you will be in a world of pain. Please, trust me I know what I'm talking about, trying to kill a big, bad ass boar with a throwing knife is a pretty sure way to end up pushing up daisies. I've seen boars charge in spite of a couple of gunshot wounds, it takes a good shot from a powerful gun to stop them, a throwing knife will not do.
Please, think about what you're going to do. When I hunt boars with a knife I use a double edged 9" blade, leaf shaped, with a good guard and grip. I stab the beasties and drive the whole blade as deep as I can, I usually get bruises on my hand from hitting the guard so hard. Knife hunting has a long tradition in some countries, it is a great way to hunt, but throwing a knife at a boar just seems like knocking on Darwin's door.
Please think about what you're going to do.