Bystander conflict is a situation in which employees are hindered in their work by parties not involved in the primary process. Public service employees and emergency care workers, such as ambulance employees and firefighters, often encounter this kind of conflict with potentially far-reaching detrimental effects for public or patient safety. Unfortunately, until now, bystander conflict has hardly received scientific attention. In this paper, we will present the results of an experiment (Study 1) and a simulation study (Study 2). Taken together, the results indicate that bystander conflict is negatively related to the affective, behavioural, and cognitive outcomes of individuals. Higher levels of bystander conflict were associated with more negative and less positive feelings (Studies 1, 2), unfavourable bystander appraisals (Studies 1, 2), and lower levels of performance (Study 2). Additionally, Study 2 revealed that bystander conflict was negatively and indirectly related to positive affect and performance through cognitive capacity. We investigated the moderating role of resilience, in order to provide insight into potential factors alleviating these negative associations. In both studies, resilience alleviated the negative associations of bystander conflict. Overall, the results of the two studies provide a first step towards a theory on bystander conflict.