Concussion and Head Injuries in Soccer: Research Trends, Knowledge Structure, and Emerging Themes.

Introduction: Soccer is the world's most widely played sport and exposes athletes to a distinctive combination of acute concussion risk and repetitive head-impact exposure. Player-to-player contact, aerial challenges, falls, and purposeful heading all contribute to the spectrum of head impacts encountered in the sport. Although the literature has expanded substantially, its development, disciplinary structure, geographic distribution, and evolving research priorities have not been comprehensively characterized. This study maps the research landscape of concussion and head injury in soccer and identifies major contributors, knowledge clusters, and emerging themes. Methods: A bibliometric analysis was performed using the Web of Science Core Collection. The search combined soccer/football title terms with concussion, traumatic brain injury, and head-impact topic terms and retrieved 2,134 publications. Publication year, citation counts, Web of Science categories, source journals, authors, institutions, countries, cited references, and keywords were analyzed. VOSviewer was used to construct co-authorship, institutional, country, co-citation, and keyword networks. Results: Publication output increased from fewer than 30 papers annually during most of 2002-2011 to a peak of 198 publications in 2020, with output remaining substantially above early-period levels thereafter. The 10 most-cited papers accounted for approximately 13.8% of citations in the retrieved corpus. Sports Sciences was the leading Web of Science category, and the Journal of Neurotrauma was the most productive source journal. Network analyses demonstrated distinct collaborative and thematic clusters spanning biomechanics, concussion assessment, neuroimaging, repetitive head impacts, and neurodegeneration. The United States occupied the most central position in country collaboration networks, while several soccer-dominant nations were comparatively peripheral. Conclusion: Research on concussion and head injury associated with soccer has expanded markedly and has become increasingly multidisciplinary. However, the present dataset also reveals an important methodological and interpretive issue: because the search included the unqualified title term "football," some American-football literature entered the corpus. Thus, the prominence of American-football papers should not be interpreted solely as evidence that soccer research is derived from American football; it also reflects search-term overlap. Within this limitation, the networks identify persistent gaps in soccer-specific research, particularly sex-specific evidence, youth education, international representation, and validation of objective measures of cumulative head-impact exposure.