On bad dogs and bad dog owners.
I had dogs and I have been bitten by dogs since I was 3 years old, so my approach to a situation like this would have been different. After the first bit on my pooch, I would have dropped it and go after the offending dog, control it (whatever use of force may be need it) and punish it for his behavior because it is clear the owner did not instill discipline in the canine.
Would I’ve been bitten? Fair chance, but again, it is something I have experienced before and it would not freak me out. And if the owner of the offending pooch has issues about the way I dealt with his problem, there is always a couple of thousands of dollars in vet bills I could gladly take him to court for.
This looks like a fenced dog park. In which case, every dog owner goes in at their own risk. When I used dog parks, I always chose times of day when no one else was there. If someone else showed up, I left. I wasn't there to let my dog play with other dogs (and exchange parasites or diseases), but to give them a chance to run free.
If out in the general public, I never hesitated to defend my dogs (who I kept on leash) from other dogs that weren't. Or to shame their owners if they were around. But that rarely needed to happen, since I had German Shepherds.
Guy in the cap missed several opportunities to kick the crap out of the offender. I carry when I am walking and I usually, but not always, also have pepper spray. Would not hesitate. Had an owner of a yapper tell me, "But she's just a little thing." Yeah. All that means is the stitches will be lower on my leg. I love dogs, but have no desire to be the victim of some owner's lack of responsibility. It's a shame the dog has to be the one paying the price.