You guys are assuming that a dog can win that fight. I hear about tonnes of dog / human fights, but how often is it that the human dies?
Our standard of losing in a fight with a dog is getting a whole heap of stitches. It could never win against a grown person, but it can tear a chunk out of your leg or arm before it's done.
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If it's just one angry dog, no matter how big, I'd probably just accept that I'm going to get afew stitches, and attack the dog. Just keep your hands in fists without fingers out and bash the sh1t out of its eyes...
Most of the danger with a single dog attacking some arbitrary person, is its initial impact. Imagine 150lbs hitting you in the chest at high speed. It's gunna knock you over. Once you're on the ground you're pretty well forced to protect your head and neck with your hands. So take away it's initial momentum(run at it, instead of it at you), and you've taken away its advantage.
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If it's a pack of angry dogs...Well...the intelligent thing to do would be to stand there, or slowly put something in between you and the dogs. I'm naturally a "take no b.s." type of person, so I might just kiss the cross I wear around my neck, and go tear the crap out of the biggest dog there.
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It's all speculative of course. I've been in my fair share of fights, and I know how fast things can go wrong, but the fight is generally awarded to the one with the most energy and aggression, not the biggest.