Data Methodology - The Managerial Merry-Go-Round

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Data Methodology & Known Limitations

This page explains where the data comes from, which rules decide what you see in the visualization, how the data was checked, and where it is still incomplete. (Status: September 2026)

What is in the dataset

The dataset covers 35 clubs, five in each of seven leagues (England, France, Germany, Italy, the Netherlands, Portugal and Spain), for every season from 1955/56 up to and including 2025/26. That is 2,485 club seasons. For each season it records the manager of the season, whether the club won the league title, a national cup or a European trophy, and, for most clubs, every manager who was in charge during that season.

How it started: generated data, checked by hand

The first datasets, for England and the Netherlands, were built through trial and error with Google's Gemini and stored as CSV files. After the data moved to a Firestore database, the other five countries were generated with a single standardized prompt that produced structured JSON. The prompt is shown below as a record of how the project began; every value it produced has since been checked against other sources, as described further down.

"Genereer een JSON-array met de managergeschiedenis voor de volgende 5 Portugese voetbalclubs: Sporting CP, Benfica, FC Porto, Boavista, en S.C. Braga. Instructies: Periode: De data moet elk seizoen van 1955/56 tot en met 2024/25 bevatten. Volledigheid: Zorg ervoor dat elk afzonderlijk seizoen voor elke club aanwezig is in de output. Sla geen jaren over. Elke club moet precies 70 seizoenen in de data hebben. Manager: Gebruik voor elk seizoen de manager die het grootste deel van dat seizoen de leiding had. Gebruik geen interim-managers. JSON Structuur: De output moet één enkele, grote JSON-array zijn. Elk object in de array vertegenwoordigt één seizoen voor één club en moet de volgende structuur hebben: { "club": "Naam van de Club", "land": "Portugal", "seizoen": "YYYY/YY", "coach": "Volledige Naam van de Coach", "nationaliteit": "Nationaliteit in het Engels", "nat_code": "ISO 3166-1 alpha-2 landcode (in kleine letters)", "landstitel": "Y/N", "nationale_beker": "Y/N", "europese_prijs": "Y/N" } Voorbeeld van een object: { "club": "Sporting CP", "land": "Portugal", "seizoen": "2023/24", "coach": "Ruben Amorim", "nationaliteit": "Portuguese", "nat_code": "pt", "landstitel": "Y", "nationale_beker": "N", "europese_prijs": "N" } Start nu met het genereren van de volledige JSON-array."

The manager of the season

Each season has one manager of the season. His tenure decides the colour of the block: red after one full season, then increasingly dark green. The rule is strict and applied the same way to every club:

Season window: a manager counts for a season if he was in charge for at least three days between 1 August and 20 May. Summer appointments and very short caretaker spells outside that window do not count. Because of the pandemic, the window for 2019/20 runs until 31 August.
Longest in charge: the manager of the season is the one with the most days in charge within that window.
Never an interim: caretakers and interim managers are shown, but can never be the manager of the season. At Ajax in 2023/24, for example, Maurice Steijn is the manager of the season, although interim John van 't Schip was in charge for longer.
Full seasons: the tenure count that sets the colour only includes seasons in which the manager was the only manager. Seasons with a change of manager are shown separately.

Seasons with more than one manager

Mid-season sackings are the heart of the question this site asks, so the current version shows them. A season with more than one manager is drawn in red and split into one bar per manager (up to five), and the info pane lists everyone who was in charge, in order, with interims marked.

These line-ups were compiled in September 2026 from the lists of managers on Wikipedia in six languages (English, Italian, Dutch, German, French and Spanish), using the language in which each club's list is most complete. Where possible the source is stored as a fixed Wikipedia revision, so that later edits to a page cannot silently change the data. The raw lists were then normalized: joint managers were split into separate people, sporting and technical directors were removed, and the precision of each date (day, month or estimate) was recorded.

Complete line-ups are now known for 2,158 of the 2,485 club seasons, and 559 of those seasons had more than one manager. For 27 clubs every season is covered. For AS Monaco, Athletic Bilbao, Boavista and S.C. Braga the available sources give only years, not dates, so their seasons are shown as single blocks. For Paris Saint-Germain, AZ, FC Twente and Borussia Mönchengladbach some early seasons are still missing.

Verification in September 2026

Comparing the line-ups with the manager of the season stored in the database brought 66 seasons to light where the two did not agree, or where the sources themselves were unclear. Each of these was resolved individually, with the Wikipedia lists, the manager histories on Transfermarkt and other club sources side by side. For a few cases API-Football was used as an additional check. Transfermarkt's manager histories were read only for the roles "Manager" and "Caretaker Manager" and processed with the same season window as above. As a result, the manager of the season changed in 56 seasons.

The 2025/26 season was added in the same way: line-ups with exact dates from Transfermarkt, and the winners of every league, cup and European competition taken from the official competition websites.

Automated tests now check the data. They make sure that every club season appears exactly once, that every manager entry is exactly one person, that each country has at most one champion per season, and that all previously flagged seasons remain resolved.

Trophies

Trophies were checked against the lists of winners of every national league, national cup and European competition. In September 2026 the league champions were also compared with final tables from football-data.org. This found two errors in 2024/25 (the Premier League and Serie A), which were corrected. That source also lists Ajax as first in the Eredivisie of 2019/20, a season that was abandoned without a champion; the dataset follows the official decision and has no champion for that season.

European trophy: the European Cup and Champions League, the UEFA Cup and Europa League, the Cup Winners' Cup, the Inter-Cities Fairs Cup and the Conference League.
National cup: the main domestic cup. In countries with more than one cup, such as England (FA Cup and League Cup), winning either counts.
One of each per season: a season counts at most one league title, one national cup and one European trophy. A season in which a club won both English cups therefore counts one cup.
Credited to the manager of the season: trophies count for the manager of the season, even if another manager was in charge when the trophy was won. Zinedine Zidane, for example, took over Real Madrid halfway through 2015/16; the Champions League of that season counts for Rafael Benítez, who was in charge longer.

Photos

Manager photos come from Wikimedia Commons, where photographers publish them under free licences. In September 2026 all photos were checked: 34 missing portraits were added, photos of the wrong person (a botanist, a tennis player, a writer and a singer who share a name with a manager, among others), team photos and photos from websites without a free licence were removed or replaced, and links to deleted files were cleaned up. Of the 828 managers, 584 now have a photo. Instead of a credit under every photo, the maker and licence of each one are listed on the Photo credits page.

Known limitations

Close calls: when two managers were in charge for a similar number of days, small differences in dates decide who is the manager of the season. For older seasons, dates are sometimes known only by month.
Missing line-ups: as described above, four clubs have no line-ups with dates, and four clubs miss some early seasons.
Missing data (Portugal): for Boavista and S.C. Braga, the data for several seasons between the 1950s and early 1970s could not be verified. These seasons are marked as "No reliable data" in the visualization.
Merged clubs: Paris Saint-Germain, FC Twente and AZ are merger clubs. For the early seasons in the dataset, the data shown belongs to their predecessor clubs (Stade Saint-Germain, S.C. Enschede and AZ'67, respectively). In the explorer these clubs are marked with an asterisk, and the info pane names the predecessor for those seasons.
Names: managers appear under the name they are best known by, which can be a nickname (for example "Petit" for Armando Teixeira).
Historical nationalities: nationalities are recorded as they were at the time, which explains countries that no longer exist, such as Yugoslavia.

Spotted an error?

With more than 2,400 seasons there will still be mistakes. Every page has a "Report an error" link at the bottom, and in the explorer you can report an error for a specific season: click a block to lock it, then use the flag in the info pane. Every report is checked against the sources.

Future development

The next steps are line-ups for the clubs that still lack them, and more clubs and leagues, starting with Belgium. (Status: September 2026)