In this series of two articles, we connect complexity theoretical frameworks of ecological dynamics and enactivism to initiatives for learning to play tennis advocated by USTA and Tennis Canada. These initiatives were inspired by the International Tennis Federation commitment to reduce the complexity of learning tennis by rescaling the game for children and novice players. This article suggests that tennis teaching is shifting from a skill and drill approach to one embracing a play-practice-play idea in line with Ecological Dynamics. Considering players as dynamic and adaptive sense-making beings, this article outlines how these initiatives create the conditions to embrace insights from motor learning in relation to a constraints-led approach, and enactivism from embodied cognition. This first article concludes with applying an enactivist teaching strategy called modification by adaptation to these tennis initiatives, showing how players of diverse ability can challenge each other, promoting more game-based dynamic learning. [For part 2, see EJ1370957.]