English Hares and Italian Tortoises: When do Goal-scorers peak?

Yesterday, I walked into a New York bar just in time to see Francesco Totti wheel away in celebration. He had just sent Torino's goalkeeper Joe Hart the wrong way from the penalty spot to score his 250th Serie A goal. Totti has scored more Serie A goals than any other player in the last sixty years. He has also now scored in 23 consecutive Serie A seasons.  He turns 40 on Wednesday.

An interesting feature of Totti’s career is that he scored nearly half of his goals since he turned thirty. He didn’t even really get going until his late twenties, a slow burner. Contrast this with Wayne Rooney: 173 EPL goals so far, half of which were achieved by the age of 24. A fixture in the Man Utd team since the age of 18, he is now, at 30, perceived to be much a diminished force.

So when do strikers normally reach their goal scoring peak, and how rapidly do they decline thereafter? Do the hares that establish themselves early in their career tend to burn out faster than the tortoises that have the more sedate start? To investigate, we need to look at the goal-scorer's aging curve.

The goal-scorer's aging curve

The aging curve of footballers – how their ability and effectiveness changes with age – is notoriously difficult to measure. How do you know when a defender has reached the peak of his career? Defending is very much a team responsibility, and great defenders can often play in attack-minded teams that concede quite a few goals. Football is team sport and it is difficult to isolate the contribution of individual players.

However, the main job of a striker is to score goals, which is a convenient a barometer by which to judge the ebb and flow of a career. By looking at how their average goals per game ratio varies over their careers, we can investigate the age at which they hit peak goal scoring ability. Obviously there are lots of factors in play: the number of chances created by teammates, the standard of the opposition, changes in position. But if we take a large enough sample of players some of this should average out, enabling us to measure the effects of aging.

I collected the career statistics of the 50 highest goal scorers in England, Italy and Spain since the 1992/93 season. This gave me a sample of 146 players (there’s a bit of overlap between the countries). In every year of their career, I measured the goals-per-game ratio for each player[1]. After a bit of smoothing and rescaling[2], I calculated the average profile across the 146 strikers. The result is shown in Figure 1.

The plot shows how scoring rate depends on player age for the most proficient goal scorers to have played in England, Spain and Italy in the last 25 years. The curve has been scaled so that the peak – which is at age 26 – is equal to one. The shaded region is indicative of the level sampling uncertainty.

Figure 1: The goal-scorer's aging profile: the rate at which the goals/game ratio varies over an elite striker’s career. The curve is scaled such that the peak is equal to 1. 

Footballers are generally perceived to peak in their mid-twenties, between the ages of around 24 and 29; the data in Figure 1 supports that notion. However, what surprises me is that the slope of the curve is not steeper as we move away from the peak in either direction. The profile implies that at the ages of 18 and 32 strikers are scoring at 80% of their peak rate, which seems quite high.

Part of the explanation for this is related to sample selection: I’m looking at the top goal scorers over the last 25 years and so their careers at the top level of football were naturally quite long (basically a form of survivorship bias). However, there is another, more interesting reason. Figure 2 shows the ageing profiles for the EPL and Serie A players separately. There is a striking difference (hah!).

Figure 2: The aging profiles for top strikers in the EPL and Serie A. Both curves are scaled such that their peaks are equal to 1. The is a clear preference for youth in the EPL and experience in Serie A. The grey region indicates sample uncertainty.

Players that play in the EPL score a substantial portion of their goals in their early twenties. There is a slow increase in the strike rate up to the peak at age 26 and then a more rapid drop-off. Serie A players are the opposite: they score predominantly in the latter half of their career. While their peak is only a year or two later than EPL players, there is a more gradual decline thereafter. The La Liga players – in case you’re wondering – are between the two.

I interpret this as resulting from the difference in the style of play between the two leagues. The frenetic pace of the EPL lends itself to the energy and potency of youth, while the slower, more cerebral style of Serie A requires the game intelligence which is, generally, the product of experience. 

This hypothesis is supported by player appearances. By the age of 22 the top strikers in the EPL have played 22% more league games than their Serie A counterparts. However, over the age of 30, strikers in Serie A play 18% more games. Young players get more opportunities in the EPL, older players are preferred in Serie A. An age difference is also evident in the national teams: at Euro 2016, the average age of the England squad was 25.4; the average age of the Italian team was 28.4. 

The relentlessness of the EPL may also expedite a player’s decline, while the more forgiving tempo of Serie A slows it. Hence strikers play on for longer in Italy. Totti was the youngest player ever to captain a Serie A team; he is also the oldest player to score in the UEFA Champions League.

In his autobiography, England manager Sam Allardyce suggested that players are at their best for around a decade. If we accept this as true, then perhaps it is no surprise that Rooney’s days as a leading goal scorer appear to be over. Of course, Ryan Giggs was able to remodel his playing style enabling him to play for Man Utd into his forties. Will Rooney also learn how to become a tortoise?

[1] If a player made less than 15 appearances in a given season, I ignored their ratio for that season. If a player played in multiple leagues in his career, I also only consider games played in the top divisions of England, France, Spain, Germany and Italy.
[2] Each profile is rescaled so that the goals/per game ratio is equal to 1 in the peak year. This is because I wanted all players to be weighted equally when taking the average profile over the sample. Before rescaling, I lightly smoothed the profiles with a moving average. 


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