Body armor is right. Next time you got a big ol' hog on the ground, one with a shield, take out your fancy knife and try to stab through it! On the big tough ones you will probably have to turn the knife around, hold it like a psyco, and use quite the whip motion to get through it. On the softer ones you could do it with a sharp stick.
The ones I've encountered, it seems that the plate was more "inside" the skin. Kind of like hitting a scapula, but on autopsy no scapula hits were encountered. Just thick, cartlegeous, fat, and skin. There ribs are a joke compared to there tough spots.