Decentralized punishment can maintain contributions to a public good at a high level. This positive effect holds even for situations involving inequality in punishment power, meaning that the relative costs for punishment differ between persons. We extend this line of research by examining the additional influence of instability of and thus potential competition for punishment power in public good experiments. As in previous research, inequality is operationalized by assigning the role of a ‘strong player’ to one group member, who can punish others at a reduced cost compared to other players. Instability is operationalized by the fact that the role assignment can change across rounds and is contingent on behavior in previous rounds. Three experiments show that under unequal, unstable (punishment‐) power, individuals behave more competitively and engage in a race for power resulting in detrimental effects for the group. Specifically, we find that (i) unstable power goes along with a disproportionate use of punishment; (ii) not inequality by itself but rather the combination of instability and inequality causes this effect; and (iii) this excessive use of punishment is found not only when the role of the strong player is assigned to individuals who previously behaved rather selfishly but also when prosocial behavior leads to the top, speaking for a generalizability of our findings. Implications for organizational settings are discussed. Copyright © 2016 John Wiley & Sons, Ltd.