Hogs like many wild animals and even some domesticated animals can be notional. Not an everyday occurrence but Hog attacks aren't all that unusual either. But like Doublenaut mentioned. mostly when wounded, trapped or cornered.
A buddy of mine made the local Newspapers, he killed an attacking Hog with his knife. The hog had been hit by brush hog and wounded. My buddy and the farmer were tracking it when it attacked. Too close to shoot, he used his knife. Thankfully he had a pair of leather pants on, got bruised up but not opened up.