If the cat is truly feral, and not someone's free-roaming pet, it really it detrimental to just release it back into the wild. Feral cats reproduce, spread disease, and destroy wildlife. As a veterinarian, I'll tell you that it is also my opinion that they don't have much of a life. They are usually ill and flea-ridden. I would trap the cat and take it to the Humane Society to be euthanized. Just make sure you're not doing in someone's pet. I know not everyone agrees with me on this. Many of my clients are kind people who trap, spay or neuter and release feral cats. This is just my opinion.