Game researchers have extensively studied how players form long-term social organizations such as guilds and clans to accomplish complex tasks such as raiding in online games. Few studies have been done to understand how temporary teams (or pickup groups) composed of strangers fulfill complex tasks. Riot Games' League of Legends, a team-based competitive online game, is played by two temporary teams. Players must collaborate with strangers in a relatively short time (about 30-50 minutes). How do players interact and collaborate with their teammates in temporary teams? To answer this question, we conducted an ethnographic study within the League of Legends community. We conducted 30 semi-structured interviews with experienced players. We found that rich social interaction exists within temporary teams. Players want to collaborate with strangers through communication and coordination. They discipline their own ways of interaction to facilitate collaboration. They try to exert influence over their teammates. We further discuss design implications for facilitating collaboration among strangers.