Social acceptance is a key variable in predicting protest against infrastructure projects. However, the social mechanisms that explain how low levels of social acceptance lead to mobilization have received less attention. This article aims to understand one particular element of mobilisation: the role of social interaction in the neighborhood. We use unique, unobtrusive data of protest participation to study the neighborhood effect of public opposition. Our case study focuses on opposition against a highway project in the city of Antwerp, Belgium. Based on a large, geocoded database with addresses of protesters and activists, we build a model to analyze activism and mobilization in neighborhoods. We control for the distance between the neighborhood and the project, as well as the socio-demographic profile of the neighborhood. As expected, we find that distance has a significant impact on the occurrence of protest. Contrary to expectations, the aggregated socio-demographic profile of a neighborhood is not significantly related to levels of opposition. However, the presence of social capital and the presence of active protesters are good predictors of protest participation in the neighborhood. These findings support theories on the collective efficacy of neighborhoods.