Several years ago, I punched a dog owner after they let their canine nearly savage a cat to death, while I was out walking.
I got the cat away in time and thankfully all it suffered was a shock but afterwards I said “Next time put it on a leash, there is a sign that says keep your dogs on leads”, they responded with a “sod off”, so I punched them.
They were in their late teens or early 20’s, and just so surprised. Thankfully I had nothing on that could identify me and wasn’t driving so, I just avoided that area for a while to make sure that plod didn’t give me any hassle, as I had no interest in being arrested for doing a public service.