I have had problems just as you describe. Being a 370lb Caucasian house-ape that has arms like tree trunks, I normally do not have any problems.
It seems like people are just plain dumb sometimes, and age is not discriminate.
I had a large problem with teenagers walking through my yard, and walking their dogs through it as well. I have a 175lb pittbull rotweiller mix, and while being a big baby, there are certain things you do not do.
1. Walk a strange dog through the yard.
2. Walk through the yard if you are a Stranger.
3. Attempt to hit my wife when he is out on a leash with her.
After quite a while of putting up with this crap ( tresspassing ect.) I get a call from my wife one afternoon at about 3:45PM. She says that someone was in the yard, she asked them to leave, and when the person got an attitude and swung at her, my pitt/rott (Named "Tank" BTW) jumped up, grabbed this girls arm, and dragged her to the ground. He didn't break the skin, but he held her to the ground for about 5 seconds, and let her go. By the time I got there, the police, animal control, and a group of this retard's friends were yelling at my wife, who was trying to talk to the cops about the attempted assault. Of course, there was a lot of jeering about the supposedly "vicious" dog. I told the Cop that if he was provoked, its not his fault or my wifes. He got the entire story from my wife, and asked to see the dog. I brought the dog out, and of course he was nice and friendly. The cop turns to the girl who swung on my wife and proceeded to explain that a dog that size could have RIPPED HER ARM OFF if he was so inclined, and it was her own damn fault. Animal control was about to take Tank away for testing (just to be sure) when i brought out the tape from the camera I had installed a week prior. it clearly showed this girl getting right up into my Wifes face, and swinging at her, and what the dog did. It was enough for the girl to get a trespassing ticket along with Disorderly conduct.
Tank didnt get taken, as all of his shots are up to date and he is very healthy. The girl had the balls to come back with some of her "homies" about an hour afterwards, making a ruckus out on the sidewalk. I stepped out and asked them to leave, they got a bit heated. I just looked at them and told them that if they felt the need to be nasty, we could do it that way. I'm a big guy, and fucking crazy too. Most people know that. That was the end of that little saga.
I think I would have dragged the little cocksucker out of the car by his middle finger had I been there.....and then proceeded to take him back to his mommy . Thats just me....and I probly would have gotten in a bit of trouble...LOL
Jeses...that was long winded. /hijack