Toxic behaviors in online gaming such as flaming and harassment have been gaining attention from the research community, yet little consensus has formed about what constitutes toxic behavior. Game developers usually maintain a classification system of toxic behaviors, which oftentimes fails to reflect the dynamic and developing forms of toxicity. In this paper, we consider toxic behavior as situated action, and seek to establish a taxonomy of toxic behaviors from a player perspective in League of Legends, currently one of the largest Esports games in the world. Our findings include five primary types of toxic behaviors, as well as five contextual factors that could lead to toxic behavior. In doing so, we provide a holistic, detailed account of toxic behavior in a team-based competitive gaming context, highlight the role of player perspective in explaining toxic behavior, and extend existing scholarly discussions on toxicity and moderation.