Personal Informatics (PI) are information systems that allow people to process activities with the usage of information technology, aiming to produce informational products (data) either for themselves or for others. Technologies that enable PI are becoming increasingly popular, assisting people in collecting personally relevant information about their body and their behaviour. In sports industry nowadays, a great variety of PI wearable tools offer support to athletes and training staff to improve their performance. An example of such tool is the Electronic Performance and Tracking Systems (EPTS), which is a combination of hardware and software that facilitates the collection, storage, analysis and management of professional athletes’ fitness and health data. Although significant and broadly used, EPTS have not yet received much attention from researchers and, thus, understudied. Therefore, the purpose of this research paper is to explore and understand how professional football athletes and training staff make sense of the use of electronic performance and tracking systems (EPTS) in their everyday training and work. The paper explores perceptions, benefits and challenges that professional football athletes and training staff experience when using EPTS. For this, an interpretive qualitative focused ethnographic study was conducted. The data were collected through direct observations in the field and semi-structured interviews from purposively selected Greek professional football athletes and Greek training staff that use wearable EPTS in their everyday training and work. The collected data were analysed thematically to conclude to five themes, which represent the research findings. A theoretical framework, which is built upon relevant literature from the informatics field along with the theory of sensemaking was used to understand, interpret and discuss the research findings. The research findings show that EPTS have radically changed the football daily routines for both professional football athletes and training staff members enabling them, and their football clubs, to improve individual and team performance. The use of EPTS has reshaped football athletes and training staff members’ identities, making them more data driven and more accurate. EPTS build trust between professional football athletes and training staff offering them the evidence they need to justify decisions, instructions, and actions taken respectively. Visualization tools for presenting insights need to be further improved with the addition of infield monitors and 3D presentations. Furthermore, it is important for training staff members to have ethical and consistent strategy on how EPTS data are derived, used and communicated. Through daily evaluation of their work, football players and training staff members are constantly improving their work identifying exemplary patterns of training and avoiding mistakes to be repeated, and in this way improve individual and team performance. The football athletes and the training staff members through communication among them, facilitated by visualization tools, are concerned with making situations, which have been collected in the form of data by the EPTS, meaningful to them. Making sense is a collaborative cognitive and ongoing process where individual football players and training staff members try to give meaning to collective experiences retrospectively. The data that are extracted from the EPTS help them in this process as they have the chance to examine them together, reflect on them, discuss them, make sense of them, share these meanings, and finally decide how to act based on them. To do this they raise past, tacit and private knowledge to make it explicit, public, ordered and simpler. In this way, the football athletes and the training staff members turn circumstances into well understood situations, which empower them to use their understanding to build more impactful experiences to improve their future performance. Thus, the research contributes to the existing knowledge on personal informatics and adjusts them to elite team sport context. It also adds to the theory of sensemaking regarding how users make sense of PI tools that are related with their everyday routines at work. In addition, it contributes to football athletes, sport training staff members, and other interested stakeholders by suggesting a model for efficient use of EPTS technology into the everyday football practices and a model of sustainable use aiming to the overall improvement of team performance. © 2022 Copyright for this paper by its authors.