  How does the team formation relates to team performance in professional video
game playing? This study examined one aspect of group dynamics - team switching
- and aims to answer how changing a team affects individual and collective
performance in eSports tournaments. In this study we test the hypothesis that
switching teams can be detrimental to individual and team performance both in
short term and in a long run. We collected data from professional tournaments
of a popular first-person shooter game {\itshape Counter-Strike: Global
Offensive (CS:GO)} and perform two natural experiments. We found that the
player's performance was inversely correlated with the number of teams a player
had joined. After a player switched to a new team, both the individual and the
collective performance dropped initially, and then slowly recovered. The
findings in this study can provide insights for understanding group dynamics in
eSports team play and eventually emphasize the importance of team cohesion in
facilitating team collaboration, coordination, and knowledge sharing in
teamwork in general.
