Witnessing peer victimization is an emotionally salient event, particularly for youth. Given that emotions influence how youth respond to social situations, the emotional experiences of bystanders may influence how they respond to peer victimization. In particular, different defending behaviors may be motivated by different emotional processes among bystanders. The current research used a novel virtual-reality paradigm, Cyberball-VR, to examine the emotional processes underlying how defending occurs in real-time. Cyberball-VR is an adaptation of the Cyberball paradigm in which participants have the opportunity to engage in defending behavior after witnessing social exclusion in the lab. Participants (N = 120) consisted of youth ages 11-14 (49% female). Self-reported data (empathic concern, personal distress, vicarious emotions) and qualitative data (noticing the exclusion and defending during Cyberball-VR) were collected. Witnessing social exclusion in Cyberball-VR elicited changes in vicarious emotions. Noticing the exclusion significantly predicted enacted defending behaviors (comforting and solution-focused), as well as increased vicarious anger. Additionally, empathy (empathic concern and personal distress) and anger interacted to predict different defending behaviors. Results indicated that how youth feel in the moment, as well as their individual tendency to respond to these emotions, influences their subsequent defending behaviors. Potential applications for Cyberball-VR and how it can be used for studying peer defending behaviors are discussed.