People who compete alone may entertain different psychological motivations from those who compete for a team. We examine how psychological motivations influence individual competitive behavior in response to a head start or a handicap when competing alone or competing for a team. We find that contestants’ behavior in both individual and team contests exhibits a psychological momentum effect, whereby leaders fight harder than trailers. However, the momentum effect is significantly larger in individual contests than in team contests and further disappears in team contests that are enriched with pre-play communication. The standard economic model, which predicts neither momentum effects nor treatment differences, fails to explain our findings. The findings can be better explained by a combination of two behavioral models: disappointment aversion and team spirit.