I have a 1.5 year old male un-neutered cat who is great.... for the most part. Ever since my upstairs neighbor (and their pit bull) moved out, I've been letting him go outside during the day (with supervision) into a small enclosure in the backyard- its about 20 by 20 feet with 5 foot wooden fence. I know that there are other cats in the area that might visit every now and then, but honestly I've never seen one in the three years that I've lived at my apartment. Today, I let Sam out and watched him explore the backyard - as usual, but when I went to pick him up to bring him back in, he hissed at me and clawed my face. I put him back down and let him run around for another 15 minutes and then I tried to get him again, he rubbed up against me and let me pet him and then suddenly he hissed at me and attacked me again! I ended up having to scare him back into my apartment with a broom! Once he was inside he seem OK again. WHAT'S GOING ON???