A widely accepted role of the sport coach is to elicit positive athlete ‘outcomes’ (e.g., enhanced performance, wellbeing, confidence etc.). However, evidence concerning the relationships between coaching practice and athlete outcomes is fragmented leaving researchers and practitioners little clarity to inform their work. Through a systematic search protocol and critique conducted through the lens of critical realism, this paper provides an overview of 208 English language peer-reviewed studies investigating relationships between coaching practice and athlete outcomes, and how current approaches may facilitate or hinder our understanding. Findings indicate research has predominantly utilised quantitative, cross-sectional or correlational approaches, with limited explicit consideration of paradigmatic influences. Discourse is dominated by psychological theorising (e.g., motivation), with studies generally employing single-method research designs and engaging a singular perspective (e.g., the athlete). Thus, we have a broad understanding of some coaching practice variables that may influence athlete outcomes (i.e., the what), but lack more interpretive and causal explanations of how and why practice is influential, accounting for the inherently complex and multi-faceted nature of the coaching process. Future research directions are proposed, which it is hoped will extend our understanding of the often intricate, heterogeneous influence of coaching practice, supporting coach educators and coaches.