This caused an incident for me just this week. I came over the top of a short hill and was met by an owner on one side of the road chatting to someone and the dog at the end of a stretched leash on the other side of the road. It was rather good that the dog was smallish because the leash was low enough to be pushed down under my front wheel. The leash retriever handle jerked out of the guy's hand and went sliding rapidly towards the dog.
The guy did call out that he was sorry so I gave him a cold "No problem".