Haralabos Voulgaris bought Spanish second division side Castellón after leaving the NBA and Dallas Mavericks. Now, he is slowly building a culture of data-driven decision-making.
Haralabos Voulgaris has always existed on the margins of the sports world.
He witnessed the NBA’s analytics revolution not at its vanguard, but just behind it. He built models, watched untold hours of basketball, and searched relentlessly for an edge to beat the markets until the edges he kept finding started to draw attention. He took his analytical mind and those models to the Dallas Mavericks, where he became director of quantitative research and development.
Voulgaris eventually wanted to buy an NBA franchise and run it on his own terms, but billionaires kept outbidding billionaires, and the goalposts (or hoops) kept moving. So, he turned his attention to a place where he could find even more inefficient markets: European football.
From the sidelines to centre stage, Voulgaris now spends his days in Spain running CD Castellón after becoming the club’s maximum shareholder in 2022. An hour north of Valencia on Spain’s east coast, the club currently sit 11th in the second division after spending the last decade and more in Spain’s lower leagues, even dropping as far as the fourth tier.
Volugaris spent years watching basketball like a codebreaker. He studied substitution trends, clock management, the rhythm of in-game adjustments. His brain is trained to spot patterns the rest of us experience only as vibes. In Castellón, he’s applying the same logic: rebuild the system, trust the data, ignore the noise.
But he isn’t doing the rich-guy-plays-football-manager bit. He’s taking the long way around.
Off the field, there’s a new 23,000-square-metre training complex in the works with pitches built like a mini stadium, a space for the women’s and youth teams. There are new sponsorship deals and a renewed energy on the terraces as Castellón fans ready themselves for a push up the Spanish football pyramid.
On the field, the data has translated into something tangible, too. Castellón were promoted to Spain’s Segunda División just a year after the takeover. They play a high-energy, occasionally reckless brand of football. Since their return to the second division, they’re inside the top three in a number of football’s most important attacking metrics.
Revolutions don’t always necessary look like revolutions. This one is taking the form of a slow and steady march towards progress.
Castellón are on the move. And it’s all being driven by data.
Garbage In, Garbage Out
With the proliferation of data in sports, it has become easy to tune out. Too many dashboards, too many metrics, and not nearly enough time to figure out what any of them mean. In football, as in every other industry that’s been “disrupted”, the assumption is that more data equals better decisions. And yet, as Voulgaris told Opta Analyst, that assumption might be exactly what’s holding most clubs back.
Data used in the wrong way is worse than not using data at all.
“I think the rush for clubs to use data without really understanding sampling or variance can actually widen the gap. The sharper clubs, the ones who understand how to work with data and have experience making decisions with data are the ones best served to lean heavily on data, in my opinion,” he said.
With that in mind, then, the objective isn’t to specifically become the most “data-driven” club in the world.
“The goal is not to get every decision right, because that is not realistic. The goal is to consistently make better decisions than your peers and to keep improving the process that leads to those decisions,” he added.
“It’s an imperfect science.”
The Imperfect Science
Much of Voulgaris’ approach, and the things he is trying to do right as the owner of his own football club, comes from knowing how dysfunction looks up close.
“When I was with the Mavericks, the front office was, in my view, far too disorganised,” he said. “The culture of decision-making was chaotic. The owner was the de facto final decision-maker, but he wasn’t directly involved in doing the work behind those decisions. Instead, he’d constantly poll different people with varying levels of influence.
“What I did like, though, was that if you were willing to really document your reasoning and show the work behind a player move, you could convince him. The downside was that you’d often spend more time debating or trying to persuade someone who hadn’t done the analysis than actually improving the team.
“That experience shaped how I run things at Castellón. I value open input, but decision rights are clear, and I avoid the endless debate loop that comes from unclear authority.”
But soccer brings up it’s own set of problems that basketball doesn’t have.
“Results dominate everything,” Voulgaris said regarding the challenges that face him as a football owner.
“And because matches are low-scoring and full of variance, people often judge decisions by outcomes and small samples instead of process. In football, a single goal can swing the entire narrative around a performance. You can play well for five matches, create more chances, control the game, and still lose two of them because of a deflection or a missed finish.”
Results-Driven Business
After five games this season, three defeats and two draws, Voulgaris had seen enough to make a change. He sacked Johan Plat for Pablo Hernández, who had been working for the club’s second team and just been promoted into the Segunda RFEF (fourth tier) with them.
So far, from a data perspective, Voulgaris has to like what he is seeing. The former Leeds United maestro has improved Castellón’s xG per game to 1.69 per game from 1.52. They were already high up the list in xG under Plat (7th) but Hernández has given them the third-best xG per game in the league.
Maybe more importantly, they now have the fourth-best xG against in the league (0.78/game). Under Plat, they were conceding double that amount per game (1.60) for the third-worst mark in the league.
It’s early days and Voulgaris won’t be getting ahead of himself given the uncertainty around small sample sizes, but Hernández has them looking like genuine title contenders. They have the best xG difference per game under his watch (+3.66) and they are unbeaten in four games (W3 D1).
They play forward fast, as the graph below shows. And this can lead to a lot of randomness in results even if the performances are good. That’s why understanding the underlying trends is so important.
“That randomness makes it hard to separate performance from result,” Voulgaris said. “Over time, the noise can drown out good decision-making, because people are reacting to the last scoreline instead of the underlying trend. It takes discipline and conviction to stay focused on process when short-term variance from casuals are screaming at you to change direction.”
So when fans are baying for the manager’s head and the media refuses to let it drop, it takes courage and calm to stay the course. Voulgaris’ convictions are rooted in an attacking brand of football, a brand of football built to excite.
He previously told The Guardian: “I love our style: we don’t play for ties. When we played Deportivo, they defended. We went ahead, they attacked. They scored, defended again. It was comical to me. That’s the inefficiency. Three points for a win, one for a draw, zero for a loss, it’s the most basic thing.”
They’ve spent just 41% of their games with the scores level, one of the lowest in the keague. This is a direct result of a simple heuristic: it’s better to try to win three points and end up with zero than settle for one.
A Sustainable Style
The style, in itself, is productive even if the results haven’t followed because playing exciting, attacking football gives your players a platform to shine, which in turn draws the eyes of scouts from bigger clubs.
“In the NBA, losing is rewarded with a better draft position, while in football, losing brings the threat of relegation,” he added. “Player trading is also a core function in European football, both sporting and financial, whereas it doesn’t exist in the NBA.”
Castellón’s style has led to player sales, enough to fund the entire project. This summer they sold Daijiro Chirino, a player they signed from PEC Zwolle two years ago, to Almería for a significant profit. Jozhua Vertrouwd, whom they signed for free after leaving Utrecht U21s, joined Rayo Vallecano for another massive profit.
The process of filtering players and highlighting potential transfer targets might be deductive but sometimes it can be intuitive.
“There have been several cases where I was watching video of a player the data had highlighted, and another player on the same team caught my eye,” Voulgaris recalled. “Sometimes that second player ends up being the real discovery. The data leads you to the right place, but you still have to stay alert when you are there.”
A Novel Approach To Scouting
The transfer market is a main pillar of Castellón’s model, and it’s no surprise Voulgaris has a novel, data-led approach to discovering new talent.
It is an almost heretical approach to scouting.
“We do not rely on in-person scouting. Our process starts entirely with data. We identify players through our models, and only after that do we watch film to understand their style, decision-making and personality on the pitch. The data leads, the video confirms.”
With clubs scouting traditionally, they are limited by their ability to watch players and it reduces the scope of potential signings. Castellón have no such limitations. If you don’t need to worry about the logistics or travelling to and from games, the entire world is open to you from a scouting perspective.
“With reliable data feeds, you can effectively scout every league in the world,” Voulgaris continued. “The challenge is not access, it is translation. Context is crucial. You need to understand the role the player was being asked to play and how that role shapes the data.”
Voulgaris has not been shy in bringing in players from different leagues. Castellón have used players from 15 different countries this season, the most in the league. They continue to replenish their squad with players just before or at their peak with an eye on potential future sales.
Culture Clash
Spanish football coaching has been exported around the world. There are more players from Spain playing across Europe’s top five leagues than any other nation. Four managers in the Premier League are Spanish; no other nation has more representatives in the dugout.
Their methods work in that sense but it hasn’t always translated to innovation within Spanish football itself. A country that has renowned academies and produces world-class coaches at an industrial level doesn’t really need to look outside itself for inspiration and innovation.
But that’s not to say it works perfectly.
“It is easier to change minds when you own the club because you can set the culture from the top,” he said, explaining how he deals with this culture clash. “People either align with that approach or they tend to move on naturally. I do not force anyone to think a certain way, but embracing data and open-mindedness is part of how we operate, and that will not change.”
Voulgaris has a simple heuristic for how he thinks about everything the club are doing: “If we weren’t doing it like this already, is this how we would start?”
The professional gambler turned football club owner never realised his dream of owning an NBA franchise, but he is very much in control at Castellón, putting his data-driven theories to the test.
Not every decision has been the right one, but Voulgaris’ strike rate so far is impressive.
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Inside Spanish Football’s Most Innovative Project — Led by a Former NBA Number Cruncher Opta Analyst.
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