At all seems to have started when Grizzy came to the sanctuary. Groucho took an almost instant dislike to Grizzy, so much so that he'd go out of his way to find him and start a fight. Newcomer Grizzy was already stressed and miserable about his environment (not to mention he'd recently lost an eye), and so it was easy to feel sorry for him and angry at Groucho when Groucho threw him off the top of the cages. And so Groucho had what was to be the first of many "time outs."
And then somewhere along the way, Groucho started going after other cats. He'd get so wound up that he couldn't calm himself down if he wanted to. The time outs became more and more frequent until he had to spend all his time either in a cage in the doublewide or in an outdoor run out the back. Staff even tried a special collar with medicinal properties that were supposed to help calm him, followed by a prescription medication. Nothing seemed to help.
Helping even less are some of the cats he's attacked in the past who, being cats, hold a grudge. Greyson in particular has been observed hanging around Groucho's cage and taunting him.
Fortunately, not all have forsaken Groucho. Loving, loyal Salty often drops by to check on him and even asks to go in his cage and sit with him from time to time. He also still has some human friends who haven't given up on him, who will go into his cage and sit with him (he particularly likes a little company while he eats his dinner) or give him a brush.
Salty visiting Groucho
We still don't know exactly what caused the change in Groucho's behavior. Staff have looked into discernible causes such as possible pain from bad teeth, etc., but so far the change remains a mystery. We may never know for sure.
Towards humans, Groucho's still much as he ever was. A little wound up sometimes because he'd really like to be let out of that cage, but still the kind of cat you can go and spend some time and share some cuddles with. He's even got his own special brush in his cage which he loves being groomed with.
I don't think he understands why he's become a bad boy any more than we do. So, as the sign on his cage says, "Please visits & brings treats & lovin'"