Defensive behavior is defined as a behavioral response to threatening situations for survival and body safety of oneself and others (Pulkkinen, 1987; Wrangham, 2018). Defending is a prosocial behavior defined by the intent to help victimized individuals (Eisenberg and Spinrad, 2014; Lambe and Craig, 2020). Lambe and Craig (2020) proposed that defensive behavior can be conceptualized as a multidimensional behavior, suggesting that solution-focused and aggressive defending are ways in which individuals defend directly while reporting to authority and comforting are ways in which people defend indirectly supporting the victim. Together, these four behaviors reflect different ways in which individuals can defend others from victimization. Reflecting on the social value of defensive behavior, some questions come to mind and need to be answered. Generally, prosocial behaviors are defined as intervening actions that are preceded by the direct observation or inference of another's a negative state (Dunfield and Kuhlmeier, 2013; Warneken, 2013; Dunfield, 2014; Eisenberg and Spinrad, 2014; Tomasello, 2019). Prosocial behaviors rest on the ability (i) to recognize that another is having a negative experience, (ii) to understand what an appropriate response would entail, and (iii) to act with the motivation to intervene. Dunfield (2014) claimed that within the general domain of prosocial behaviors there are three distinct types (helping, sharing, and comforting), which are responses to three negative states: instrumental need when individuals cannot complete a goal-directed action; material desire, when individuals do not have access to resources; emotional distress when individuals experience a negative emotional state. Each of these negative states can be alleviated by a different prosocial behavior, such as helping, sharing, or comforting, respectively. These prosocial behaviors rely on different social-cognitive assessments, such as goals for the helping, desires for the sharing, and emotions for the comforting. These three types of behavior show unique ages of onset, dissociable developmental trajectories, and distinct associations with individual difference factors early in life. Recent research has emphasized the multidimensional nature of prosocial behavior and has fueled the current debate on the psychological mechanisms underlying prosocial actions in early childhood (Dunfield, 2014; Paulus, 2014, 2018). According to Dunfield's model (2014), we believe that defending action can be among prosocial behaviors as a subtype for the following reasons: (a) it is triggered by the recognition that an individual is in a state of emotional distress, and (b) it is aimed to alleviate this negative state. To alleviate the emotional distress, defending action involves a specific negative action against the aggressor to protect an individual victimized. Unlike the comforting action, defending behavior implies a direct action against the aggressor as a consequence of a negative evaluation of the aggressor's antisocial action. Furthermore, there is no doubt that defensive behavior, like other prosocial behaviors, contributes to social well-being, strengthening the positive peer group experiences across development (Dirks et al., 2018). What is the underlying motivation for defensive behaviors? What elicits this behavior? How are these behaviors triggered in the first years of life? The present article aims to answer these questions by reviewing recent evidence on defending behaviors in the second year of life.