I read this really funny (well, only funny cuz it didn't happen to me) article in the San Francisco Chronicle a couple days ago. For those of you who didn't read it, I think you'll enjoy it:
So this woman takes her pitbull to Golden Gate Park and she gets the bright idea to let her PITBULL off the leash. A nearby mounted police officer (they have mounted cops in SF?) riding on a horse named AAA Andy (awesome name) sees her unleashing the dog and hollars to her to put the dog back on the leash. The woman takes notice, but unfortunately, so does the pitbull. The pitbull immediately decides that the horse, AAA Andy, must die, and bolts towards him. Before the officer can react, the dog is attacking AAA Andy who freaks out and throws the officer onto the ground, hurting his back and neck. The woman runs over and tries to wrestle her dog away from the horse, but is rewarded with a hoof to the face. She collapses onto the ground next to the officer. Then, AAA Andy takes off full gallop while being chased by the pitbull. Half a mile away, another officer receives the distress call sent out by the first officer and spots the horse running at him full tilt while a by-stander shouts, "Watch out, it's that damn dog!" The officer manuevers himself in between the horse and the pitbull and attempts to kick the dog down while it tries to take another bite out of AAA Andy. After a few unsuccessful attempts, the officer pulls out his Barretta and shoots the dog who scurries injured into the bushes. Afterward, the first officer and the woman are hospitalized and AAA Andy and the pitbull are sent to the vet.
I believe everyone was okay in the end. So there you go. And yes, this stuff ACTUALLY HAPPENS.