"Footedness" is a concept you're probably familiar with. Players almost always naturally prefer to dribble / shoot / pass with a certain foot. Total ambidexterity (being as comfortable using one foot as the other) is rarer, but is common enough at the top level.
One of the ways in which we can quantify footedness for a player is looking at how many shots or goals the player scores using one foot vs. the other. However, this isn't that meaningful for us because the majority of the time, we can see with our own eyes which foot a player prefers.
On the other hand, footedness of teams is more interesting to me. Here I've looked at which teams prefer one foot over the other or are ambidextrous, using a new metric I've called the "Ambidexterity Index" (AI). The source for all data described here is Understat; full credit to them.
Note: This section can be skipped if the math doesn't interest you. The gist is that an AI of +1 implies "perfect" right-footedness, an AI of -1 implies "perfect" left-footedness, and an AI of 0 implies ambidexterity.
A perfectly ambidextrous player/team is assumed to have an equal number of shots/goals with either foot. This means that on a plot of right-footed shots/goals (RF) vs. left-footed shots/goals (LF), a data point on the line y = x implies perfect ambidexterity. Data points on the y- or x-axis imply perfect right- and left-footedness respectively.
The "ambidexterity angle" θ formed by the (LF, RF) data point on such a plot will be θ = atan2(RF, LF).
- Perfectly ambidextrous:
θ = 45° - Perfectly left-footed:
θ = 0° - Perfectly ambidextrous:
θ = 90°
The AI is a measure of how much the RF-LF angle deviates from a perfectly ambidextrous angle (θ = 45°), scaled to the range (-1, +1). On this scale, AI = +1 implies "perfect" right-footedness, AI = -1 implies "perfect" left-footedness, and AI = 0 implies ambidexterity. This scale makes visualizing "one-footedness"/ambidexterity easy to understand and straightforward, as you will see in the forthcoming plots!
AI = (θ - π/4)/(π/4) = (atan2(RF, LF) - π/4)/(π/4) = ((4/π)*atan2(RF, LF) - 1)
AI = (θ - 45°)/(45°) = (atan2(RF, LF) - 45°)/(45°)
For the "Shot Ambidexterity Index", RF and LF are the number of right-footed and left-footed shots respectively. Similar method for the "Goal Ambidexterity Index".
In general, I think Shot AI is more insightful into footedness than Goal AI because Shot AI has more data to work with (there are many more shots than goals).
The images below are plots of Total Shots/Goals vs. Shot/Goal Ambidexterity Index for each league and season in Understat's database. Since there are so many data points, plotting the points for all leagues in a certain season and all seasons for a certain league were not possible due to difficulty in labelling each point. The "Line of Ambidexterity" is drawn along a Shot/Goal AI of 0.
Generally, the higher up a team is located on the plots, the more "accurate" the Shot/Goal AI is, since it means the Shot/Goal AI was able to incorporate "more" data.
| 2014-15 | 2015-16 | 2016-17 | 2017-18 | 2018-19 | |
|---|---|---|---|---|---|
| Bundesliga | Plot | Plot | Plot | Plot | Plot |
| La Liga | Plot | Plot | Plot | Plot | Plot |
| Premier League | Plot | Plot | Plot | Plot | Plot |
| Ligue 1 | Plot | Plot | Plot | Plot | Plot |
| Serie A | Plot | Plot | Plot | Plot | Plot |
| 2014-15 | 2015-16 | 2016-17 | 2017-18 | 2018-19 | |
|---|---|---|---|---|---|
| Bundesliga | Plot | Plot | Plot | Plot | Plot |
| La Liga | Plot | Plot | Plot | Plot | Plot |
| Premier League | Plot | Plot | Plot | Plot | Plot |
| Ligue 1 | Plot | Plot | Plot | Plot | Plot |
| Serie A | Plot | Plot | Plot | Plot | Plot |
| Plots | |
|---|---|
| Bundesliga | Plot |
| La Liga | Plot |
| Premier League | Plot |
| Ligue 1 | Plot |
| Serie A | Plot |
| Plots | |
|---|---|
| Bundesliga | Plot |
| La Liga | Plot |
| Premier League | Plot |
| Ligue 1 | Plot |
| Serie A | Plot |
Here are images displaying tables of the top 10 most right-/left-footed and ambidextrous teams in terms of Shot/Goal AI.
- Top 10 Ambidextrous Teams (Season-by-Season, Shot AI)
- Top 10 Right-Footed Teams (Season-by-Season, Shot AI)
- Top 10 Left-Footed Teams (Season-by-Season, Shot AI)
- Top 10 Right-Footed Teams (Season-by-Season, Goal AI)
- Top 10 Left-Footed Teams (Season-by-Season, Goal AI)
- Top 10 Ambidextrous Teams (Overall, Shot AI)
- Top 10 Right-Footed Teams (Overall, Shot AI)
- Top 10 Left-Footed Teams (Overall, Shot AI)
- Top 10 Right-Footed Teams (Overall, Goal AI)
- Top 10 Left-Footed Teams (Overall, Goal AI)
- Bundesliga 2014-15: Hamburg are the only Bundesliga team to be predominantly left-footed.
- Torino 2014-15 are remarkable: they only scored 1 left-footed goal out of 36 goals in that entire season. This makes them officially the most one-footed team across all seasons (Goal AI).
- Liverpool 2018-19 are the most ambidextrous team across all seasons (Shot AI) - they shot exactly 244 times with either leg. In fact, they are the only perfectly ambidextrous team across all seasons (Shot AI).
- Bundesliga: Although Schalke and Bayer 04 Leverkusen also had seasons in which they were left-footed, the only Bundesliga teams to have been left-footed overall are Hamburg and Fortuna Düsseldorf.
- La Liga: Barcelona's Shot AI of 0.0009 is remarkable - they're far and away the most ambidextrous team examined. I didn't have time to investigate it further, but I do wonder how much their Shot AI would change if Messi was excluded.
- Premier League: Middlesbrough stand alone as the sole left-footed team out of all Premier League sides since 2014.
- Ligue 1: Not a single Ligue 1 team was left-footed overall. Gazelec Ajaccio's claim to fame is that they are the only team out of all teams examined to be perfectly ambidextrous in terms of Goal AI!
- Serie A: With three overall left-footed teams (four if you consider Goal AI), Serie A is officially the most left-footed out of the top 5 leagues.
- It's already known that the majority of players are right-footed, but it's interesting to see that reflected in the data. Only 7 teams were primarily left-footed overall, and that too with a maximum Shot AI of just 0.14 (only slight left-footedness).
- 5 out of the 8 overall left-footed teams (Goal AI) are currently not playing in the top 5 leagues anymore. Clearly, this means that having more left-footed players than right-footed players ensures your relegation. Better tell your right-footers to take a lot more shots.
In case you're interested, here are links to the full spreadsheets that contain all of the AI data.
AI Data - Season-by-Season Spreadsheet AI Data - Overall Spreadsheet
Thanks for reading! Hope you enjoyed it. Let me know if you have any questions.