The increasing national diversity of coworkers has no consensus on its impact on performance. Using a team's predominant nationality as a proxy for national diversity and national identity, there is robust evidence that it affects team and individual performance. Detailed worker‐level data from a highly globalized industry, association football, show a nonlinear relationship between performance and the predominant nationality of a team's roster. As the number of members from the predominant nationality increases, performance declines. However, beyond a threshold level, performance rises. It follows that performance benefits from national diversity when the predominant nationality is small and from national identity when it is large.