Performance analysis in soccer is considered an important tool for evaluating team behaviours and improving team outcomes. In general terms, a common approach is to associate success with various game-related performance indicators to identify playing styles that increase and/or decrease the probability of team success. For example, ball possession rates (Bradley et al., 2014; da Mota et al., 2016), passing variables (Hughes and Franks, 2005; Wallace and Norton, 2014), shots on goal (Hughes and Franks, 2005; Lago-Penas et al., 2010), specific playing formations (Bradley et al., 2011; Carling, 2011), and defensive variables (Santos et al., 2017; Vogelbein et al., 2014) have all been associated with team success. These relationships and the overall performance of a team however, can also be influenced by external 'contextual' variables such as match location, opposition quality, and match status (i.e. winning or losing) (Lago and Martin, 2007; Taylor et al., 2008).
Additionally, game-related variables have been used to characterise styles of play in professional soccer leagues worldwide (Fernandez-Navarro et al., 2016; Gollan et al., 2018; Lago-Penas et al., 2017). A team's 'game style' has been defined as a combination of identifiable strategies and tactical behaviours that are regularly repeated and rehearsed by a team during specific phases of a match and from game to game (Hewitt et al., 2016). The game style is based on quantifying elements involving average player and/or ball speed, duration and number of skilled actions, and location of possession and movements (Hewitt et al., 2016). Recently, including contextual variables in performance analysis has added resolution to our understanding of player interactions and team dynamics that can impact playing styles under a variety of conditions. These include, for example, strength of the opposition (Yang et al., 2018), current match score line (Sarmento et al., 2018), playing venue (Gomez et al., 2018), or a combination of all three variables (Almeida et al., 2014; Bradley et al., 2014). The results of these studies have shown altering these conditions can impact the preferred playing patterns of a team, and highlight the importance of considering these contexts when preparing for games or characterising playing styles. Moreover, this type of research can shed light on potential mechanisms of why styles change in predictable patterns in specific contexts.
Over the past decade numerous playing styles have been described for soccer (Sarmento et al., 2018). Many of these are based on analysing game events within specific 'moments', or periods of play, to indicate relative dominance in particular moments. These include play patterns such as 'build up' styles (extended periods of controlled possession (Collet, 2013; Kempe et al., 2014)), counter attacks (rapid progression of the ball to optimise player imbalance (Gonzalez-Rodenas et al., 2016; Tenga et al., 2010b; Turner and Sayers, 2017)), defensive transitions (the actions occurring immediately after a team loses ball possession and their efforts to regain possession or inhibit opposition offensive actions (Almeida et al., 2014; Santos et al., 2017; Vogelbein et al., 2014)), and set pieces (for example, corner kicks (Yiannakos and Armatas, 2006)). Efforts to characterise tactical team play have included player positional coordinates in line with offensive and defensive 'principles of play'. For example, how effectively teams stretch or create space in offence, or compress and confine when defending (Folgado et al., 2014). Derivations of these metrics involve quantifying the central location of a team's players or 'centroid' and analysing its position relative to other variables, for example, the opposition's centroid, when goals are scored or during transitional play (Frencken et al., 2011). However, whilst dissecting a game into phases to analyse a team's strengths, weaknesses and characteristic playing style has been reported, it is only relatively recently that a definition of game style using the moments of play framework has been published (Hewitt et al., 2016). Furthermore, no studies have used the aforementioned framework in performance analysis to investigate how styles can be influenced by contextual elements in soccer. In fact, there are numerous ways researchers have characterised playing styles without reference to a consistent methodology (Fernandez-Navarro et al., 2016). Consequently, it has been problematic to compare styles across leagues, time, changes in coaching and playing personnel, in addition to analysing game styles as a function of contextual variations. This study will investigate the influence of contextual variables on soccer playing styles from the English Premier League (EPL) using the moments of play framework (Hewitt et al., 2016).
Moments of play
Playing styles within this research were defined using the moments of play framework described by Hewitt et al. (2016). The moments of play framework quantifies playing patterns by dissecting a game into five distinct periods, or moments. These moments can be used to analyse a team's relative performance during key periods of match play. Based on the degree of ball control for one team, the moments are identified as; set pieces (SP), established offence (EO), transition into offence (TO), transition into defence (TD), and established defence (ED).
All 380 games from the 2015-16 EPL season were included for analysis. Across the season, each team plays the opposition once at home and once away, resulting in all 20 teams playing 38 League games. The dataset used in the current research was also used in a previous study conducted by Gollan et al. (2018), and a detailed methodology describing the use of game-related variables to quantify game style is described in this earlier study. Briefly, 96 game-related variables recorded from all matches were supplied from a commercial sports data provider (OptaPro). The reliability of...