Agree that top down commitment is necessary but another key ingredient is when the players take ownership of team success. Certain leaders on the team hold others accountable and demand excellence from them. A guy like Dansby Swanson comes to mind. He led by example first and set the tone day in day out. It shouldn't always have to come from the coaches.
Nick Saban stated that he knew his team got it when he heard upper classmen telling freshmen "we don't do it that way at Alabama."