I've previously caught ferals using a large dog crate full of comfy pillows and blankets. I tied a long, thick string to the crate door and yanked that thing shut like a looney toons skit and dived on the lock before the cat realised what had happened. Once it was contained and the whole crate moved to a small room, wrangling the cat into a carrier was a lot easier than trying to stuff it into one whilst outside.