Transfer market activities and sportive performance in European first football leagues: A dynamic network approach

Professional football is a globalized game in which players are the most valuable assets for clubs. In this study, we explore the evolution of the football players’ transfer network among 21 European first leagues between the seasons 1996/1997 and 2015/2016. From a topological point of view, we show that this network achieved an upper limit expansion around season 2007/2008, thereafter becoming more connected and dense. Using a machine learning approach based on Self-Organizing Maps and Principal Component Analysis we confirm that European competitions, such as the UEFA Champions League or UEFA Europa League, are indeed a “money game” where the clubs with the highest transfer spending achieve better sportive performance. Some clubs’ transfer market activities also affect domestic performance. We conclude from our findings that the relationship between transfer spending and domestic or international sportive performance might lead to substantial inequality between clubs and leagues, while potentially creating a virtuous (vicious) circle in which these variables reinforce (weaken) each other.职业足球是一项全球化运动，球员是俱乐部最具价值的核心资产。本研究探究了1996/1997赛季至2015/2016赛季间，21个欧洲顶级联赛的足球运动员转会网络演化历程。从拓扑学视角出发，本研究表明该转会网络在2007/2008赛季前后达到扩张上限，此后网络连接愈发紧密、结构愈发稠密。本研究采用基于自组织映射（Self-Organizing Maps）与主成分分析（Principal Component Analysis）的机器学习方法，证实欧洲赛事（如欧洲冠军联赛（UEFA Champions League）、欧足联欧洲联赛（UEFA Europa League））本质上属于"金钱游戏"——转会投入最高的俱乐部往往能取得更优异的竞技表现。部分俱乐部的转会市场运作同样会对其国内赛事成绩产生影响。基于研究结果，我们得出结论：转会投入与国内、国际竞技表现之间的关联，可能会加剧俱乐部与联赛间的实质性差距，同时可能形成良性（恶性）循环，使得上述变量彼此相互强化（削弱）。