Yup, that is bumblefoot and can cause an internal blood infection if not treated. If you want to attempt treatment yourself, it will mean removing that plug which is holding pus in there, daily cleaning & nurturing of the wound area and PenG injections into the breast to help with infection for 7-10 days....possibly longer depending how bad the infection is. I would recommend a vet too.
As a reminder, staph is contagious to other chickens and people. You will want to do a thorough cleanout of the coop, roosts, etc. And wear gloves while working with the bird.
Jody