Toxic behaviors are pervasive in online games and can be harmful to building a positive online environment. Guided by the social identity model of deindividuation, this study represents one of the first efforts to examine the antecedents of toxicity in team-based online games using longitudinal behavioral data. It fills two important gaps in existing research, by 1) exploring non-verbal and behavioral dimensions of toxicity, and 2) examining team-level in addition to individual-level predictors. Employing a large-scale behavioral dataset from the popular game World of Tanks, we found that, in general, experienced and skillful players are more likely to commit toxic behaviors. Teams that are losing, or have a high internal skill disparity among their members tend to breed toxicity. In addition, this study provides empirical evidence that toxicity is contagious among players, especially toxic behaviors in one's own teams and in clan battles.