House Cats Acting Strange! Please Help!

[teh calico kitty]

I really don't know how much information you need, so I'll just tell you what I know ^_^
I have two house cats- one female (saphie), one male (butters). Butters had been fixed, but our female hasn't been. They never go outside, they're strictly indoor cats. But for the past week, we've been bringing them outside every couple of days on harnesses, to let them get some more fresh air, and walk around a little. Well today, we brought them both outside, and about 30 minutes after we brought them back in, Saphie stated to violently attack Butters. They play fight sometimes, but this was just ridiculous. They were hissing and growling, and they even bled a little. Butters (who is younger than Saphie) didn't start it and was trying to get away, but Saphie wouldn't leave him alone. I'm having to keep them separated tonight.

I just really don't understand what could be wrong with them, they've never done this before. Saphie didn't even react this badly when we first brought Butters home as a kitten. What should I do? Will they return to normal in a little while? Please help me~  

[Cowgirl-with-heart]

it might be that she doesnt recognize him,they go mostly on scent,so him smelling different might have freaked her out.