The ‘Sports and Friendships’ study was conducted between 2021 and 2023 (Franken et al., 2023). Its aim was to understand the development of multiple dimensions of students’ social relations throughout student life, and its consequences for their sport participation and academic experiences and outcomes. The study follows two cohorts of students at a research and vocational university of a Dutch city (Cohort I: N = 92, Cohort II: N = 655). We mapped the important transitions they experienced (e.g., leaving the parental home), the accompanying changes in their egocentric networks (e.g., newly formed ties), and employed multiple methods to map their sports activities (i.e., survey self-reports, behavior trace data). The codebook document describes the kinds of data that have been collected in the context of the ‘Sports and Friendships’ study.