We had the same problem recently. This tuxie kitty kept coming into our yard and terrorizing our kids. Halo (15 lbs) ran. Cammie (10 lbs) hissed and ran. Pepper (6 lbs) fought her off several times and suffered some injuries. After our next door neighbors experienced the same problem with this cat, we watched out for her and found out where she lived. (Her name is Princess -- and she's anything but!). I approached the owner and told her that I needed to make sure that Princess had all her shots and checkups because she was causing injuries. The owner was very nice about it and assured me that Princess' shots are all up-to-date and I asked for her vet information in case MY cats injured Princess. (Not, that I thought that was going to happen since the bigger 2 are weenies and Pepper was barely holding her own). That kind of shocked her a little and she has kept Princess in her yard ever since then. It's a little different here because by this time next month, we'll have several feet of snow on the ground so none of the kitties will be going out. So, I recommend you find out where this kitty lives and talk to them in a kind, friendly way and see if you can work this out. Of course, if they are jerks, then no telling what will happen to this poor kitty.