When signing new players, it is tempting to make a judgment based on their past performance – after all, the only concrete data we have about a player’s performance is what they have done in the past. However, ideally we should base our decisions on a player’s future forecast performance, not his past performance.
Our previous research has indicated that football players reach their peak performance years roughly in their mid-20s on average. If we sign a 27-year old player who has just had three great seasons, it is very well possible that those three seasons were the best ones he will ever have, and that his performance levels will start declining as he gets older.
Of course, not every player will have the same career trajectory. Some players will start declining earlier, others won’t really reach their maximum potential until later. Applying a blanket rule to all players is likely to make us miss the variation from player to player.
A good example of a player who peaked very early in his career is Kelechi Iheanacho. When he broke through at Manchester City, in 2015, it was hard to imagine him becoming anything other than one of the best strikers in the league. After all, almost no 19-year olds have 7 starts, 26 appearances, and 8 goals playing for a team that reached the Champions League semi-finals. He seemed to be Agüero’s presumptive heir. Alas, it was not to be. He only scored 4 goals in the next season, before moving to Leicester City, where he scored 3 league goals in his first season, and finally 1 league goal in 2018/19. He hasn’t made a league appearance in 2019/2020 yet.
On the other end of the spectrum, his Manchester City partner Fernandinho has arguably only reached the best years of his career in his 30s, under the management of Pep Guardiola. Whereas many of the Manchester City players of his generation (Hart, Zabaleta, Kompany, Kolarov, Yaya Touré) were slowly phased out after Guardiola started managing, Fernandinho stepped up to the challenge and established himself as the lynchpin of City’s midfield, the best midfield in world football. Fernandinho actually played more league minutes in the 2017/18 season, when he turned 33, than in any other season in his career.
Our view of a player’s potential has to be more nuanced than looking at just his age; we can’t use a one-size-fits-all approach. Even though the average peak age for football players is 25, Iheanacho’s peak years are undoubtedly behind him at age 23. Conversely, Fernandinho was yet to make any of his 53 international appearances for the Brazil national team at age 25 – most of his potential was still unrealized, and he was a smart signing by Manchester City even at the age of 28.
Using 21st Club’s Player Contribution Model, we compare a player’s career trajectory to every other player in the world to find his closest comparisons and forecast when he is going to reach his peak performance – we can understand whether each player is more like Iheanacho or Fernandinho. It is not enough to know the potential of the average player; to make the best decisions, we must know the potential of each specific player we are considering.