Background: The number of people with one or more chronic diseases is increasing, but this trend could be reduced by promoting physical activity. Therefore, in 2012, the Dutch Ministry of Health, Welfare, and Sport introduced Care Sport Connectors (CSCs), to whom a broker role has been ascribed. The defined outcome of CSCs role is an increased number of residents participating in local sports facilities and being physically active in their own neighbourhood. To realize this, primary care and sports professionals need to collaborate, and local sports facilities and neighbourhoods need to offer accessible physical activities for people in the locality, including people with one or more chronic diseases or at increased risk of chronic disease(s). Adequate scientific research is needed to assess CSCs' impact on: 1) connecting primary care, sport, and physical activity and 2) increasing the number of residents who engage in physical activity to promote their health. Methods and design: To study the role and the impact of CSCs, a longitudinal multiple case study will be conducted, in nine municipalities spread over the Netherlands, from 2014 until 2017. A mixed methodology will be used to perform action research and process evaluation. Study I focuses on the expected alliances of CSCs and the preconditions that facilitate or hinder CSCs in the formation of these alliances. The study population will consist of intermediary target groups. A literature review, interviews, focus groups, and document analysis will be undertaken. Study II will concentrate on lifestyle program participants to identify health and physical activity behavior changes. For this purpose, interviews, literature studies, a Delphi study, fitness tests, and questionnaires will be used. Discussion: Linking and integrating results gained by multiple methods, at different levels, will provide a validated assessment of CSCs' impact on connecting the primary care and sports sectors. This will reveal changes in residents' physical activity behavior, and ...