The impact of crowd effect on the referee bias.

This review aimed to (1) analyze whether the home advantage was diminished; (2) investigate the impact of the crowds’ support on the match outcome and team performance; (3) explore the bias of the referee without crowds. Based on the PRISMA 2020 (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines, this systematic review searched of literature was conducted in December 2022. The keywords related to soccer, COVID-19 and home advantage were used. The search returned 135 articles. After screening the records against set criteria, 28 articles were analyzed. Results showed that the absence of crowds would reduce the home advantage of teams, but the findings varied by country. Most leagues have evidence that without the support of the spectators, their technical, tactical and physical performances would be worse. The referee seems likely to be fairer when the spectators are absent. Therefore, crowd supports is an important factor affecting home advantage, the clubs can at least try to strengthen the home advantage and increase the winning possibility by encouraging spectators to enter the stadium or reducing the ticket price.本综述旨在（1）分析主场优势（home advantage）是否有所削弱；（2）探究观众助威对比赛结果与球队竞技表现的影响；（3）探讨无观众场景下裁判的判罚偏向性。依据PRISMA 2020（系统综述与元分析首选报告条目，Preferred Reporting Items for Systematic Reviews and Meta-analyses）指南，本系统综述于2022年12月开展文献检索工作，检索采用与足球、新冠疫情（COVID-19）及主场优势相关的关键词，共检索得到135篇文献。经按照既定筛选标准对文献记录进行筛查后，最终纳入28篇文献开展分析。研究结果显示，观众缺席会降低球队的主场优势，但该结论因国家而异。多数联赛的相关证据表明，缺少观众助威时，球队的技术、战术与体能表现均会出现下滑。无观众在场的情况下，裁判的判罚似乎更为公允。由此可见，观众助威是影响主场优势的重要因素，俱乐部至少可通过鼓励观众入场或降低票价等方式，强化主场优势并提升获胜概率。