Much depends on leadership, but have you used some key tools already? Have you created an Action Item List with due dates? Have you published it? Peer pressure is a great motivator. But if it’s truly a leadership issue, it often helps to make it clear to management what the repercussions are of these people doing the work. Does that mean escalating costs? Does it mean increased customer dissatisfaction? What about the project goal? What if the team misses it? Maybe the Champion doesn’t entirely understand their role. You could send them a the roles infographic or the article about the Role of the Champion or you could ask them to spend an hour on White Belt Training. Even better, ask them to take the Yellow Belt Training to get a better sense of the improvement process as a whole.