The debate over referee bias has once again taken centre stage during the 2026 FIFA World Cup, with fans, players, and analysts questioning whether high-profile stars receive preferential treatment in crucial moments.

While controversies in soccer often rely on subjective interpretation, a new study from South Korea’s professional baseball league offers rare empirical evidence that human officials may indeed be influenced—often unconsciously—by a player’s reputation.

Researchers analysing the Korea Baseball Organization’s (KBO) Automatic Ball-Strike (ABS) system found that star hitters received fewer favourable calls once robot-assisted strike-zone decisions were introduced. The findings suggest that at least some of the advantages enjoyed by elite athletes may stem not from superior performance, but from subtle human bias. The research has implications far beyond baseball, raising broader questions about fairness in sports officiating and other fields where subjective judgment plays a critical role.

What Did the Study Find?

Researchers from the University of Michigan analysed player performance before and after the Korea Baseball Organization introduced robot-assisted strike-zone calls during the 2024 season.

Their key finding was striking:

Star hitters appeared to lose an invisible advantage once human judgement over balls and strikes was replaced by technology.

According to the researchers, prominent batters performed worse in strike-zone-related statistics after the automatic ball-strike system was introduced. Importantly, their overall hitting ability did not decline significantly, suggesting the players themselves had not become less skilled.

Instead, the researchers argue that the change reflected more consistent officiating, not weaker performance.

Study co-author Jimin Song, a kinesiologist at the University of Michigan, said that before ABS, umpires may have unconsciously given favourable calls on borderline pitches to well-known hitters.

How Do Robot Umpires Work?

The Korea Baseball Organization introduced the Automatic Ball-Strike (ABS) system for the 2024 season to improve consistency in one of baseball’s most objective decisions.

Rather than replacing the home plate umpire entirely, the system works as a decision-support tool.

The process includes:

• High-speed cameras tracking every pitch.
• Sensors calculating the ball’s exact trajectory.
• Software determining whether the pitch crossed the strike zone.
• The result being transmitted to the home plate umpire, who announces the call.

This hybrid approach removes human judgment from one highly measurable aspect of the game while preserving the umpire’s broader role in managing play.

Why Did Star Hitters Lose Their Edge?

The researchers believe the answer lies in unconscious bias, sometimes called status bias.

Humans often make slightly different decisions when evaluating individuals with established reputations. In sports, that can mean giving elite players the benefit of the doubt on close calls without consciously intending to do so.

Before ABS, an umpire facing a borderline pitch might have been marginally more likely to rule in favor of a celebrated batter than a rookie.

Once those decisions became technology-driven, that subtle advantage disappeared.

Interestingly, the study found that elite pitchers did not experience the same consistent change, likely because pitching situations vary more widely and involve fewer directly comparable borderline calls.

What Does This Mean for the FIFA World Cup Debate?

The study has attracted attention because it arrives amid renewed criticism of refereeing decisions during the 2026 FIFA World Cup.

Several controversial calls have sparked accusations from fans and pundits that officials favor:

• Superstar players
• Traditional football powerhouses
• Home or host nations
• High-profile clubs represented in international tournaments

While the Korean baseball study does not examine soccer or FIFA referees directly, it provides evidence that human decision-makers can exhibit unconscious bias toward high-status individuals.

That does not prove similar bias exists in every sport or every tournament. However, it strengthens the argument that reputation can influence judgment even when officials strive to remain impartial.

Human Bias Isn’t Always Intentional

One of the study’s most important conclusions is that favouritism does not necessarily require conscious intent.

Psychologists have long documented that people often rely on mental shortcuts when making split-second decisions.

These unconscious biases can affect judgements involving:

• Reputation
• Authority
• Experience
• Familiarity
• Social status

Officials working under intense pressure may unknowingly interpret ambiguous situations differently depending on who is involved.

The researchers suggest that technology can reduce, but not eliminate, these influences.

Can Technology Replace Human Referees?

The researchers argue the answer is no—not entirely.

Some officiating decisions are objective and easily measured.

Examples include:

• Ball or strike
• Whether a ball crossed a goal line
• Offside positioning (with technological assistance)
• Out-of-bounds decisions

Technology performs exceptionally well in these situations because the rules rely on measurable facts.

However, many sporting decisions remain inherently subjective.

These include:

• Dangerous tackles
• Intentional handballs
• Unsportsmanlike conduct
• Advantage rulings
• Time-wasting
• Player behavior

These situations require context, judgment, and interpretation—areas where experienced officials remain indispensable.

The Lessons Extend Beyond Sports

The study’s authors believe their findings apply well beyond athletic competition.

Status bias can influence decision-making in many environments where subjective evaluations matter.

Examples include:

• Hiring and promotions
• Performance reviews
• University admissions
• Classroom assessments
• Awards and recognition
• Judicial or disciplinary decisions

The researchers suggest organisations can reduce bias through measures such as:

• Blind evaluations were possible
• Standardized assessment criteria
• Greater use of objective performance metrics
• Regular review of decision-making patterns

Technology may support these efforts, but it is unlikely to replace human judgment entirely.

Why This Research Matters

Sports often serve as a real-world laboratory for studying human behaviour because decisions are carefully recorded, measurable, and frequently scrutinised.

The Korean baseball experiment offers rare evidence that changing the decision-making process can alter outcomes without changing player ability.

For leagues considering expanded use of officiating technology, the findings suggest that automation can improve consistency in objective situations while preserving fairness for all competitors.

At the same time, the study reinforces an important point: technology is most effective when used to complement human expertise rather than replace it.

The Bottom Line

The University of Michigan’s analysis of South Korea’s robot-assisted baseball officiating suggests that human officials may unknowingly favor high-status athletes during close calls. Once the Automatic Ball-Strike system standardized one of the game’s most objective decisions, star hitters appeared to lose that subtle advantage.

While the findings do not prove bias in soccer or other sports, they add scientific weight to longstanding concerns about how reputation can shape human judgment. As professional leagues continue to adopt technologies such as automated officiating, the challenge will be finding the right balance between precision and the uniquely human ability to interpret complex situations.

TL;DR

• A University of Michigan study found evidence that human umpires favoured star hitters before robot-assisted officiating was introduced.
• South Korea’s KBO adopted the Automatic Ball-Strike (ABS) system in 2024.
• After ABS was implemented, high-profile batters received fewer favourable borderline calls.
• Researchers say the findings demonstrate unconscious status bias rather than deliberate favouritism.
• The study also has implications for workplaces, education, and other decision-making environments.
• Experts emphasise that human officials remain essential for subjective decisions that technology cannot easily automate.