Football is practiced worldwide by many children and adolescents. Data from COACHKIDS+, a project co-funded by the Erasmus+ Sport programme of the European Commission, showed that at under-8 years old 476.296 male participants already practiced (Emmonds et al., 2023). However, a substantial decrease in rates of participation occurred during adolescence (12-14 years old), mainly because coaches tend to select the physical advantage players, as noted by former Manchester United Coach Sir Alex Ferguson in his biography (p. 260): “the biggest risk was that we had erred in our assessment of a particular boy and could have used his spot to work with a more talented youngster. We had to wait a little longer to see the potential in some boys, because not everyone’s physique develops at the same rate” (Ferguson 2015, p. 260). The number of youth female football participants also tended to increase during the last decade (UEFA, 2020); however, rates of dropout tend to be higher than males (Møllerløkken et al., 2015). The Women’s Sports Foundation noted that the first reason for dropout is the lack of opportunities to play (Women Sports Foundation, 2023).

Grouping players by age groups does not account for differences between participants in physical maturation. This fact explains why at under-12 years old, the height and weight range could range from 132.2 to 160.7cm and 26.0 to 55.0kg, respectively. Corresponding data for under-14 football participants is 142.8-182.9cm and 34.0-77.5kg (Malina et al., 2018). Consequently, players who are taller, heavier and advanced in biological maturation are often perceived as more talented by coaches (Malina, 2003). These players are often selected and retained systematically in the sport, which in turn is associated with coaching specialisation, training resources, and investment in their development (Malina et al., 2015). Late adolescent maturing players are consistently excluded from the sport regardless of their ability (Cumming et al., 2018).

To promote equal participation among young football players, a bio-banding approach is necessary. Bio-banding involves grouping athletes based on their biological development rather than their chronological age (Cumming et al., 2018). This strategy can also be utilized not only to retain and attract more players in football but also to enhance overall player development.