From what I hear, and was told when first I tried spearing hogs.... there are two reasons why the classic boar spear has a solid stop or cross-guard immediately behind the blade.
(1) So that the blade does not overpenetrate and skewer your faithful hound.
(2) So that the annoyed piggy is not able to come up the shaft at you, when 6 feet of spear is all that is keeping him away from your tender pink shins.
I know the feeling of surprise at how easily the spear blade penetrates.
I put it down to adrenaline. Mine, I mean, not the pig's.
Cheers.......... Cooch