Nasty boxer should have been on a leash!!!! Damn it!!

Poor Rory got attacked by a boxer yesterday! We were heading to the Fort and up over our little short cut rise and there it was. Owner had it off leash playing ball. This was an ON LEASH area of the Fort. Dog freezes, so I stop and wait for the girl to recall it and get it leashed. I didn't like the frozen look on it's face. She tries and tries, but the dog ignores her and approaches. She squeeks out something like....."she's usually friendly......." and I say it's OK, cuz Rory is a lovely dog. She has perhaps the best dog-skills of any dog I walk. Totally appropriate and awesome, just the BEST girl. In a flash the boxer is attacking her!!!! :( I SCREAM....."HEY!!!!!!".......in the loudest, firmest voice I can, which usually stops a dog, but this dog simply hesitated, looked at me and then continued it's attack. POOR RORY!!! The girl tries her best to grab the dog, but this is a boxer, they have the ability to curl into pretzels and avoid capture. Rory isn't doing anything, I see her sweet face, eyes just squinting and trying to move her head to avoid another chomp from this asshole boxer!!! I look around for a stick and see a good one, but the dog is intense and the girl is failing to get hold of it, so I take my flexi-leash handle and WHACK the dog on the top of it's head as hard as I can. Poor dog, but DAMN IT all, this is SO unnecessary!!!! I feel bad, but it worked. The woman finally grabs it's collar and pulls it away. Mumbling something about how I didn't have to yell at her dog. WHAT......THE........FUCK?????? I look at her in amazement and tell her if MY dog had been trying to rip out HER dog's throat I am quite sure she would have yelled, too!! Geesus!!!! I couldn't believe it!!!! Um, now might be the time to apologize for your asshole dog's behavior and your lack of control over the asshole dog. >:/ She did ask if my dog was OK and I tell her I don't know, yet, and will have to look her over carefully. I tell her I need her name and number, which she does give me. I am beyond furious at this point because of her comments about yelling. HELLOOOOOOOOOOO...........poor, sweet Rory was just attacked by her asshole dog..........I am going to yell. Luckily, Rory is a chow mix and has a lovely thick coat of fur to protect her, so I can not find any wounds. I feel horrible that this had to happen to her. These sorts of things can affect a nice dog and make them hesitant and even reactive in the future. I hope that doesn't happen to lovely Rory, she is SUCH a nice dog. I continue to stress to this chick as she starts to leave that her dog needs to be on a leash. She is very lucky I am who I am because anyone else would have gone straight to Animal Control to report the incident, but I don't want her dog to be quarantined for her lack of responsibility. She needs to find a private spot to exercise her dog, not a public park. I called Rory's people last night and they said she seems fine and they can't find any wounds. Phew.