Disproving the Science around Specialization

Science is subjective, not proof, as conclusions can fit different narratives around data.

A recent study concluded, “Multi-sport athletes had significantly more athletic success in their professional careers from both a statistical and an award perspective. These findings should be emphasized to youth athletes, parents, and coaches to encourage participation in multiple sports during high school,” (Sang et al., 2025). The study used a pool of NBA players to determine whether or not multi-sport high-school athletes had greater early-career NBA success.

The conclusion ignored the sample, which was drawn from a decade of 1st Round NBA Draft picks, and included 87 multi-sport athletes and 231 single-sport athletes (Sang et al., 2025). Another conclusion, therefore, would be that nearly three-quarters (72.6%) of 1st Round NBA Draft picks who played in the NBA were single-sport high-school athletes, suggesting specialization in high school enhances one’s likelihood of obtaining a professional basketball career (Sang et al., 2025). Should we emphasize to youth athletes, parents, and coaches that most 1st Round NBA Draft picks played only basketball in high school?

Same data set, different conclusions. This is the problem any time someone says, “Science says,” or “Research proves,” especially when referencing a single study. Conclusions are shaped by the authors as much as the data.

I wrote about the dangers of early specialization in Cross Over: The New Model of Youth Basketball Development over 20 years ago, but my beliefs have changed slightly as time has transpired. It is not that I believe early specialization is good, as much as I believe the research and commentary on early specialization includes other confounding variables and draws conclusions that are not as definitive as the headlines suggest. The evidence against early specialization is not as robust as the frequency of discussions, position statements, and recommendations suggests because no standardized definition exists (Mosher et al., 2020).

Specialization and early specialization often are conflated. Early specialization is not high-school students playing one sport; that is sport specialization. Only half of the research articles included in a recent review on sports specialization even mentioned the measurement of age (Mosher et al., 2020). Balyi’s (2001) original long-term athlete development paper recommended specialization after age 10 in late-specialization sports (basketball), although the most frequent definition of early specialization is specializing in a single sport “before the age of 12” (Mosher et al., 2020; Wiersma, 2000).

I found another recent research article through social media touting the benefits of late specialization and playing multiple high-school sports. The article concluded, in part, “Participation in approximately two other sports and later specialization… were characteristic of top-ranked youth players who later played in the NBA (Gulch et al., 2026). These authors surveyed top-ranked high-school players who eventually reached the NBA and matched them with top-ranked high-school players who did not make the NBA. The conclusions of “participating in two sports” and “later specialization” were used to promote multi-sport participation in high school, suggesting multi-sport participation improves one’s likelihood to reach the NBA.

Instead, the study actually found “63% of the total sample began playing on a select team by age 10”; the future NBA players joined at age 10.7, whereas the non-NBA players joined at age 9.1 (Gulch et al., 2026). The future NBA players specialized in basketball at older ages: 12.9 years old compared to 9.6 (Güllich et al., 2026). Ninety-percent of future NBA players compared to 52.5% of non-NBA players participated in organized sports outside basketball before age 14 (Güllich et al., 2026). The conclusions were correct and unassailable; the future NBA players specialized at an older age and participated in more sports. However, the ages were before high-school ages.

The content creators pushing this study as a reason for multi-sport high-school participation did not read the study or purposely misguided their followers. The study has nothing to do with high-school aged participation, other than using their national rankings during high school to create the matched pairs. The non-NBA players specialized early and engaged in less sampling, and the future NBA players were just across the early specialization threshold, on average, and sampled more at younger ages.

This study relied on surveys filled out by players with an average age of 16 at high-school basketball tournaments. Theoretically, a 16-year-old should remember his childhood of a few years ago, but surveys also can be unreliable. I messaged some former players and asked at which age they specialized. They determined specialization in different ways, as is the problem with many retrospective studies and/or qualitative research.

One said she specialized in basketball at age nine, never competed on a team in another sport, but played soccer, beach rugby, and field hockey with her basketball team during every offseason for roughy 10 years. Is a player who spends her summers (three months) playing multiple sports a specialized athlete because she competes in only one sport or is she a multi-sport athlete because she plays multiple sports recreationally? Another player answered that she specialized around age 10, but ran track and played softball in high school. Playing multiple high-school sports is the antithesis of early specialization, but she self-identified as specializing early, likely because 10 is the age when she decided basketball was her number one sport.

These answers confuse the literature. If I had simply asked at which age they specialized, both would be categorized as early specializers. However, by asking about other sports, neither is an early specializer. The manner in which questions are asked, and the number of questions affect the responses and the conclusions. Authors affect the data.

I looked for these anecdotes after another study went viral on social media. A survey of 296 NCAA Division I male and female athletes found 88% participated in an average of two to three sports as children, but participation is undefined (DiFiori, 2013). Seventy percent self-reported specializing after age 12, but specializing was not defined (DiFiori, 2013). Social media ran with the study, as science proved late specialization and playing multiple sports in high school are better, but the actual data does not show either.

In my short example (I received more responses, all of which were similar, but using two is easier for discussion), both players participated in two or more sports as children, thus fitting with the 88% of college athletes. However, both self-reported specializing before age 12, thus fitting with the 30% of early specializers. The problem was not intelligence; one of the two is arguably the smartest player I have coached in 25 years. Instead, in such a survey, the responses depended on their internalization of the questions and their experiences. Both clearly viewed specialization as the age at which they decided basketball was most important and/or joined a more competitive team, not when they stopped participating in other sports.

My research would allow me to argue either conclusion. I could conclude most college athletes self-report that they specialized in their eventual sport before 12 years old, and therefore most college athletes specialize early. I also could conclude most college athletes participated in multiple sports during their teenage or high-school years. Same data, different conclusions. Writing that most participate in multiple sports during their high-school years would lead people to believe these teenagers competed in multiple organized high-school sports, which is true of only one of the two. I can write my conclusion and headline to shape the data in whichever way I want, and I can use vague language to allow people to draw certain conclusions. Science is biased, especially the discussions.

Many from the consultant class have cited a recent study that found the “the vast majority —nearly 90% — of junior and later senior international-­level performers are different athletes,” (Güllich & Barth, 2024). This study has been used to refute early specialization and argue it is better not to be elite at young ages. Neither is addressed by this study.

First, in most sports, and especially in basketball, international competitions begin with regional U15 competitions to qualify for U17 FIBA World Championships. Therefore, at the earliest, an “international-level junior performer” is 14 years old, which is beyond the cut off for early specialization. Also, just because an athlete plays at an international level does not guarantee the athlete has specialized. Therefore, these studies do not examine early specialization directly.

More importantly, the stats are biased in one direction. “89.2% of international-level U17/18 juniors failed to reach international level as seniors,” (Güllich et al., 2023). An U15 or U16 national team has 12 players, meaning just under one player per team makes the senior level. This should not be too surprising. Every year, there is a new junior national team; this summer players born 2006-2011 will compete in international youth competitions. However, there are only 12 spots for an entire country at the senior level. This summer, players born in the 1980s could be playing with players in the ‘00s. There are not enough roster spots for an average of one per year. Ten to twelve years of national teams funnel into a single national team. Of course few of the junior players will play for a senior team.

The study also reported “82% of international-level seniors had not reached international level as U17/18 juniors,” (Güllich et al., 2023). This is the statistic showing it is better not to be good at a young age. As many say, you can be good early or good late, but not both. However, again, the numbers are distorted.

Only 18% of senior international players — one or two from a team of twelve — played international as juniors. Each age group has twelve international players. Imagine the senior national team represents a 15-year age span. Those 15 years of youth national teams with twelve players per team equals 180 potential players. Of course, not every junior player plays every summer due to injuries, improvements, and other circumstances, so roughly fifteen players per age group play some junior national team games or 225 potential players. Surely more than two of these 225 should be on the senior national team?

How many other players play? How many players do not make the junior national teams? Obviously, this varies by country. In the smallest country in which I have coached, by population, there were 20 teams at the U16 level or 240 players for the age group. Multiply that by the 15 years, and conservatively, we are talking about 3600 players. Subtract the 225 players who played for junior national teams, and we are left with 3375 who did not play for a junior national team over those 15 years. Of those 3375, ten make the senior national team.

Surprisingly, the odds actually favor those who played on a junior national team (.8% to .2%), but that is not how the data is presented. My numbers are not exact, and every country differs. I used the smallest country; bigger countries with greater participation would have more players who did not not make the junior or senior teams. The research also combines sports, and basketball may differ from these conclusions in either direction. Everyone has anecdotes to support both conclusions.

I coached numerous players who played for junior national teams in several countries, and none has appeared for a senior national team despite professional careers, NCAA National Championships, NCAA and NJCAA all-conference awards, and more. In the year they realistically would have progressed to the national team (24-26 years old), they competed against players who were 12 years older and mainstays on the national team. I once coached the most capped player in her country’s national team history, and she retired from the national team at 39 years old. A lot of players came and went while she had her national-team roster spot. Breaking in is difficult.

Just think of the NBA All-Stars not on the USA Olympic team last summer! I randomly looked up the 2018 USA U17 boys’ team. Players such as Scottie Barnes, Jalen Green, R.J. Hampton, Evan Mobley, Isaac Okoro, Isaiah Stewart, and Jalen Suggs. Is it really better not to be selected to this team? Did they fail because they played on a junior national team, but not a senior national team?

My argument is not for or against early specialization or multi-sport participation. My purpose is to point out the subjectiveness of science, as I see too many people posting that science or research proves something, when I hope the above has demonstrated the same data set can be used to conclude two opposing viewpoints, especially when using vague language and relying on adolescents and/or retrospective surveys.

My primary arguments against this research are (1) single-sport participation in high school is not early specialization; and (2) there are confounding variables that appear not to be investigated or accounted for in these studies, most notably the length of the competitive season.

Most appear to commingle sport specialization with a year-round competitive schedule, but these are two separate issues. My players in Europe generally specialize early, around 10 years old. They rarely compete in a second sport, unless they start in one sport and switch to basketball. However, they have a two to three-month offseason in the summer, and often a winter break. They specialize early, but they do not compete year-round. Players in the USA now compete year-round, although they may not specialize. Some players play year-round high school and AAU basketball, but still run track and field or play football or volleyball. The year-round competition and absence of any offseason are likely bigger causes for concern than single-sport participation during the high-school years.

I favor sampling early. I have argued every child should start with gymnastics or martial arts to develop their balance, body control, coordination, and emotional regulation. Every child should learn to swim at a young age for safety, if no other reason. After those three, I believe children should try out at least one individual and one team sport. I also believe the choice to specialize and play only one sport or to dedicate more time to one sport should come from the child, not the parent, and should come after age 10, as children likely lack the full cognitive appreciation before that age to make an intelligent decision.

Once children specialize, they need an offseason, they should participate informally in other sports and activities for fun, and they should incorporate multilateral training: A good team/club has an appreciation for movement skills and coordination development at the younger ages, and strength and conditioning by the transition to high school. These are my personal guidelines, regardless of the science or research, which, as the above demonstrated, can be biased or misconstrued to make specific points, especially when the study is paid for by an organization with a vested interest.

References

Balyi, I. (2001). Sport system building and long-term athlete development in British Columbia. Coaches Report, 8(1), 22-28.

DiFiori, J.P. (2013). Early sports participation: a prescription for success? American Medical Society for Sports Medicine National Meeting, April.

Güllich, A. & Barth, M. (2024). Effects of early talent promotion on junior and senior performance: a systematic review and meta-analysis. Sports Medicine, 54(3), 697-710.

Güllich, A., Barth, M., Macnamara, B.N., & Hambrick, D.Z. (2023). Quantifying the extent to which successful juniors and successful seniors are two disparate populations: A systematic review and synthesis of findings. Sports Medicine, 53(6), 1201-17.

Güllich, A., Meisel, P., Côté, J., Malina, R.M., Brenner, J. S., Hainline, B., ... & DiFiori, J. (2026). From youth basketball to the NBA: A matched-pairs follow-up analysis of top-ranked youth basketball players in the USA. Sports Health, 19417381261423901.

Mosher, A., Fraser-Thomas, J., & Baker, J. (2020). What defines early specialization: a systematic review of literature. Frontiers in Sports and Active Living, 2, 596229.

Sang, L., Bach, K., Feeley, B.T., & Pandya, N.K. (2025). Effects of early sport specialization on injury load management and athletic Success of National Basketball Association players. Orthopaedic Journal of Sports Medicine, 13(1), 23259671241304732.

Wiersma, L.D. (2000). Risks and benefits of youth sport specialization: Perspectives and recommendations. Pediatric Exercise Science, 12(1), 13-22.