The central point in this article is that energy system transition can be initiated by a team of individuals interacting entrepreneurially beyond their different home-grounds in business, research, or regional development. Such entrepreneurial engagement of insiders with belongings to an established socio-technical system has not been captured in prevalent sustainability transitions or entrepreneurship perspectives. Insiders have mostly been expected to act within (and not outside) of their role expectations. This study investigates who individuals initiating energy transition are, what motives they have, and how they accomplish institutional change. The purpose is to qualify a perspective that can help us better appreciate how transitions, such as in energy systems, can be initiated. The new perspective recognizes the importance of insiders, their personal sustainability beliefs, their choice to teamwork entrepreneurially, and their narratives about the initiative affecting institutional change. It explains how transition in a heavily regulated Swedish energy system can occur. Implications are drawn for research, policy and entrepreneurial teamwork.