It's been very rainy here and so I took my 2 GSDs to the fair grounds where they can run while I drive the car slow. I saw a guy out running but thought nothing of it because both of mine are very people friendly. They surprised me by running up to the guy barking. They didn't bite but the guy wouldn't stop moving and ran away with them barking and running after him. Like I said. They ran up barking but didn't bite or anything. I have never seen them behave like that before. Was it the fact that the guy was running? Did that trigger some kind of behavior?