Answering this question is an opportunity to showcase that you can work on a team and collaborate with others for good outcomes. Explaining your role and how it came about allows the interviewer to see a different facet of your abilities. A team leader is assigned in most teams. If you are typically the leader, explain what skills you have that allow for effective leadership. If not, you could elaborate on why you were not chosen or why you didn't volunteer. Your answer should illustrate cooperation, collaboration, and a willingness to contribute to add value.