I will add that loosing one or more dogs on a hog in a pen is not "sport" not to me and shouldn't be to anyone. Hog + Pen + Dog = training to be used sparingly and extremly controlled. Hog Dogging in general is not a hog in a pen, it is a hunt for wild boar and feral hogs. The sport is hog hunting that includes baying, and hog catching.
Putting a hog in a pen and letting loose a dog is not a sport. Any time a hog is in a pen the dogs are on leads and the only reason they require a hog do to be used is to make sure the dog is capable of the work on a hunt, and to make sure the dog does not target inappropriate areas such as the nose, legs, etc.
I agree with Slarti though, I don't quite see what being a vegetarian or seeing a bull fight or a slaughterhouse has to do with this, Stangsbeing against animal cruelty (which I agree loosing dogs to attack and fight a hog in a pen aka boar baiting, is animal cruelty) doesn't mean you are or have to be a vegetarian.