I can tell you that if it encounters broody Nugget, it won't be so happy to be here any longer. She is one tough mama.
We've had plenty of stray cats around and they've never bothered the chickens, so that usually doesn't worry me. I fed one for a couple of years--he made his rounds every morning and evening and was a great asset until something killed him, probably a fox or coyote, from the teethmarks on my well cover where the cat used to hide. If this is a domestic cat, albeit a humongous one, I'm not that worried about the really big chickens, but the youngsters are more vulnerable, certainly. Nugget is a force to be reckoned with when she has chicks, but it could surprise her and snatch her young one quickly.
The problem is that I'm just not 100% sure it's just a cat. I'd like to see it when it isn't speeding away at 50 mph to be sure what I'm dealing with. Could be it was just mousing that morning and put its paws on the windowsill to look in at the birds, then freaked when the screen fell over.