This work examines the extent to which people hold independent sequential events (e.g., players making correct/incorrect guesses) responsible for overall outcomes (e.g., the team winning/losing the game). Two types of events are found to garner the majority of responsibility for overall outcomes: (1) final events and (2) events that are perceived to disrupt momentum (e.g., an incorrect guess after a sequence of correct guesses). While previous research has shown that final events tend to be perceived as more responsible for overall outcomes, the current experiments are the first to document the role of perceived momentum on responsibility judgments. Specifically, we demonstrate that the effect is mediated by perceived momentum changes after the time of the event and moderated when exogenous factors (e.g., a delay between events) disrupt perceived momentum. We discuss how these findings relate to pivotality, the counterfactual simulation model, and the role of unexpectedness in responsibility judgments.