Why do people justify intergroup violence between police and protesters in social protests? This article examines attitudes towards the violence perpetrated by police officers against protesters and the violence carried out by protesters against police officers in the context of the post-social outbreak of October 18, 2019 in Chile. We evaluate the role played by the perception of injustice in the procedures and the treatment of police officers towards protesters, the evaluation of the legitimacy of police officers and group identification with protesters and police officers in predicting the justification of violence. We present the results of a survey on legitimacy and police violence carried out among adults in Chile during January 2021 (n = 2,717). Through a Path Analysis, we found that the perception of injustice in the procedures through which the police treat protesters is a key factor in predicting the perception of legitimacy of the police, especially among people who identify with the protesters. Furthermore, by reducing the legitimacy of the police, the perception of injustice in the procedures and the treatment translates into lower levels of justification of police violence and to greater levels of justification of protestor violence. The article finishes by highlighting the importance of considering the perceptions of injustice in the procedures and treatment of police officers in order to reduce the conflict between police officers and protesters in Chile.