1. Many marine protected areas (MPAs) around the world are ‘paper parks’. A key factor contributing to their ineffectiveness is non‐compliance with the rules in place. 2. This paper contributes to the existing academic discussion on ‘paper parks’ by drawing on critical regulation scholarship to develop a theoretical framework to assess and address compliance gaps in MPAs. 3. The theoretical insights are then explored using a case study of the second largest Italian MPA (the ‘Penisola del Sinis‐Isola di Mal di Ventre’), employing a multidisciplinary perspective built on both biological and socio‐legal expertise. 4. The biological study consists of a review including existing unpublished data on biological resources in the MPA coupled with new analyses on the effects of sea urchin harvesting restrictions. The socio‐legal research consists of the analysis of primary qualitative research in the form of semi‐structured interviews conducted with key stakeholders at the local and regional level in 2014, followed by two workshops (one with stakeholders and one with the general public) in 2015 to discuss the research findings collectively. 5. The results show that the Sinis MPA is not achieving its conservation goals, primarily because of actors' non‐compliance with the rules. The interviews with key stakeholders reveal a number of interlinked social, normative and calculative motivations at the basis of non‐compliance. Policy solutions are then offered. 6. This study offers a novel analysis on ‘paper parks’ that may be applicable to other MPAs experiencing similar compliance issues. Copyright © 2016 John Wiley & Sons, Ltd.