In 2013, Barcelona City Hall started the transformation of urban mobility with the superblocks proposal. A pilot project tested the grouping of nine blocks of the Cerda Plan in a unit of 400 x 400 meters, inside which traffic is restricted to neighbors. Characterized by an implementation in test phases, the intervention can be interpreted as an action of Tactical Urbanism, led by the public sector and with a small range of stakeholders. This article starts from the questioning of its relative novelty, conceptualizes Tactical Urbanism, and discusses its "phase zero" approach and the potential to combine public and community actions. The analysis focuses on the initial stages of the pilot and in the controversies generated throughout the process. Recognizing that the proposal is based on the requalification of public space, the main criticism focuses on the choice of the pilot project site and the inadequacy of the participatory processes.