German Shepherd Dog fight
Lukas, my dog, is a 160 pound . When he stands on his hind legs, he tops out at just under 6' tall. When he decides to pull- as in playing tug-of-war- whomever is on the other end gets yanked forward. When he displays his teeth, the viewer will note they are large and sharp. Mastiffs were bred as guard dogs; they are loyal and they are protective; they would be tied up at the front of a Roman house, and their job was to insure no one got past them into the house without their owner's permission.
And they were very good at their job.
Now, imagine you trying to come into my fenced yard and I didn't want you there, but as a small, elderly female, who doesn't always know where the ammunition clip for the handgun is being kept, all I have for protection is Lukas. And, in my stress-y, high-pitched voice, I indicate to Lukas I fear you. Can you imagine how Lukas is going to react?
He is going to gallump over towards you, much, much faster than you believe possible- his movement looks clumsy and ungainly, but he covers a lot of ground fast. And, after the first bark or so when he noticed you, he is going to be silent- never a good sign in an attacking dog. He will leap up at you, one hundred-sixty pounds of prime-of-life canine muscle going for your upper chest and throat; even if you are well-braced for impact, he will likely knock you over. He's built to do that and you are not built to withstand that.