The study of political contention in Spain has seen significant growth in recent years. However, the police response to protest actions remains, even today, a relatively underexplored area. This paper aims to address this gap. What factors explain police intervention during protests? When and why does this intervention involve the use of force? What are the predictors of police violence against political protest movements? To answer these questions, we draw on Protest Event Analysis (PEA) using a comprehensive, original dataset developed as part of the Disobedient Democracy (DISDEM) and Evolution of Political Contention in Spain (ECOPOL) research projects. The dataset contains information on protests held in Spain between 2000 and 2020 (n=4623). By applying statistical regression models, we aim to identify the key variables that significantly influence police intervention and the use of force during collective protests. Specifically, we examine the effects of both the characteristics of the mobilization (in terms of weakness vs. threat) and the political opportunity structures for repression shaped by the context of the protest. This includes factors such as the size and duration of the mobilization, the confrontation tactics employed, the nature of the demands, the identity of the organizers, and the political orientation of the government in power. Ultimately, our goal is to develop a framework that identifies the key factors influencing police control of protests in Spain over the past two decades.