Project management is critical to the planning and success of any project. However, unexpected events do occur, and limited information is available of how to deal with such unexpected events. There has been some research in recent years on management of unexpected events in projects, but it has typically been conducted from the perspective of the project manager and the project management team. For the most part this literature assumes that it is the project manager's responsibility to find solutions and courses of action in an endeavor to mitigate the negative effects of unexpected events in projects. However, unexpected events cannot always be resolved by one stakeholder. There is little prior knowledge about how different project stakeholder groups take actions voluntarily to accommodate unexpected events. The aim of this study is to research how voluntary stakeholder actions can lead to effective responses to unexpected events. The setting is the mega-construction project of the Vodafone Arena Stadium (VAS) in Istanbul, Turkey. The research design follows an inductive, discovery-oriented grounded theory approach. Primary data were gathered through semi-structured in-depth interviews with a sample of 20 project stakeholders who represented 15 different stakeholder groups. We find that stakeholders are able to minimize negative consequences of unexpected events using four voluntary stakeholder strategies. We further identify three properties that differentiate these categories, as well as antecedents of voluntary stakeholder actions, and discuss implications for the management of mega projects. Our findings suggest that voluntary actions of various stakeholders can lead to effective responses to unexpected events. This study advances project stakeholder research, unexpected event management and construction management research both theoretically and empirically.