The field of Sports Human-Computer Interaction (SportsHCI) investigates interaction design to support physically active individuals. Despite growing interest and dissemination of SportsHCI literature, many publications still focus on solving specific problems in a given sport. We believe in the benefit of generating fundamental knowledge for SportsHCI more broadly to advance the field as a whole. To achieve this, we aim to identify the grand challenges in SportsHCI, which can help researchers and practitioners in developing a future research agenda. This paper presents a set of grand challenges identified in a five-day workshop with 22 experts who have previously researched, designed, and deployed SportsHCI systems. Addressing these challenges will drive transformative advancements in SportsHCI, fostering better athlete performance, athlete-coach relationships, spectator engagement, but also immersive experiences for recreational sports or exercise motivation, and ultimately, improve human well-being. The paper identifies 16 grand challenges, categorized into five themes: 1) Athletic performance optimisation analysis; 2) The athlete as a multifaceted individual; 3) Human-centered design and sports engagement; 4) Technological considerations in the real world; and 5) Strategic vision on what to strive for through SportsHCI. These challenges are based on a structured five-day workshop involving 22 renowned SportsHCI researchers and practitioners. The challenges include the lack of knowledge of how interactive technology can support performance optimization, the lack of understanding of how to design interactive technologies for various parties involved in Sports Engagement, the lack of knowledge of how to design interactive technologies for the athlete being a multifaceted individual, the lack of knowledge of how to integrate biomechanics into SportsHCI, and the lack of knowledge on how to utilise real-time sensemaking of bodily performance analysis in novel digital-physical exercises. These challenges are important for the field of SportsHCI and require further research and development to address them.The field of Sports Human-Computer Interaction (SportsHCI) investigates interaction design to support physically active individuals. Despite growing interest and dissemination of SportsHCI literature, many publications still focus on solving specific problems in a given sport. We believe in the benefit of generating fundamental knowledge for SportsHCI more broadly to advance the field as a whole. To achieve this, we aim to identify the grand challenges in SportsHCI, which can help researchers and practitioners in developing a future research agenda. This paper presents a set of grand challenges identified in a five-day workshop with 22 experts who have previously researched, designed, and deployed SportsHCI systems. Addressing these challenges will drive transformative advancements in SportsHCI, fostering better athlete performance, athlete-coach relationships, spectator engagement, but also immersive experiences for recreational sports or exercise motivation, and ultimately, improve human well-being. The paper identifies 16 grand challenges, categorized into five themes: 1) Athletic performance optimisation analysis; 2) The athlete as a multifaceted individual; 3) Human-centered design and sports engagement; 4) Technological considerations in the real world; and 5) Strategic vision on what to strive for through SportsHCI. These challenges are based on a structured five-day workshop involving 22 renowned SportsHCI researchers and practitioners. The challenges include the lack of knowledge of how interactive technology can support performance optimization, the lack of understanding of how to design interactive technologies for various parties involved in Sports Engagement, the lack of knowledge of how to design interactive technologies for the athlete being a multifaceted individual, the lack of knowledge of how to integrate biomechanics into SportsHCI, and the lack of knowledge on how to utilise real-time sensemaking of bodily performance analysis in novel digital-physical exercises. These challenges are important for the field of SportsHCI and require further research and development to address them.