Performance Analysis

SSA Blog: VAR and the physicality of football

Last week saw the introduction, into competitive English football, on a trial basis, of the video assistant referee technology system (VAR). It follows last season’s successful implementation of goal line technology and is the latest in a growing number of virtual, tracking or predictive technologies introduced to support officials and referees across sport.

Arguments as to the benefits and drawbacks have been well reported. What has gained less coverage is the potential impact regarding players’ physical load during a game.


Throughout sport, rule changes and the introduction of technology have affected how the game is played and the nature of the players playing it. Tennis is a prime example.  Players often use the challenge system tactically, in an attempt to break opponents’ momentum or gain extra recovery time following a high-intensity rally.

Football at the highest level requires players to combine a number of fitness elements. It involves high intensity sprinting, accelerations, strength, an endurance base as well as the application of skill and mental agility to deal with tactical demands.

In the English Premier League, the average 90 minute game sees the ball in play for 56.17 minutes. Players are covering distances of nearly 11km per game of which over 10% is covered at high speed. But the biggest increase in activity levels has come in the number of high intensity runs players now make. Data from Barnes et al, back in 2014, showed that players were making 49% more high speed runs than in 2007 and the total distance and intensity numbers are expected to have continued to rise.

The game is undoubtedly speeding up though many have argued VAR may slow it down. What they actually mean is, VAR will impact the ball in play time. But can VAR actually increase ball in play time? Or could it lead to changes in player load and even greater physical demands?

A recent study examining the evolutionary changes in activity and recovery in Rugby League, published by Gabbett & Hulin (2017) in the Journal of Sport Sciences, showed the greatest impact on ‘ball in play’ time resulted from video referee stoppages. It also showed that ‘in game recovery’ time actually increased. So, while video referee referrals reduced the ‘ball in play’ time, it also produced greater recovery time for players, which can enable greater player load/exertion levels to be reached during games.

Could the same be a consequence of the introduction of VAR in football?

There are two areas to consider here:

  1. Will VAR reduce ball in play time?
  2. Will VAR effect in game recovery (and therefore training practices to address this)?

Until the system has been fully trialled and evaluated it is difficult to answer either of these questions. However anecdotal evidence from goal line technology points to more ball in play time as players no longer challenge the referee during breaks. This leads to play being resumed without incident. Evidence from Rugby League and Rugby union on the other hand, suggests that ball in play time has been reduced by the introduction of video technology as game time is lost during those time on and time off moments during referrals.

The really interesting analysis will be the impact, if any, on the players physical demands. Will, as we have seen in Rugby League, increased in game recovery time allow players to compete at even higher intensities once play resumes? Will more effective decision making mean less stoppages and a reduction of in game recovery? And what impact will this have regarding player preparation in order to cope with the potential physical challenges VAR might bring.  

It’s too early to know how VAR will impact player load and the physical demands of the Premier League.  As the system’s adoption increases, sport science teams will evaluate how its introduction impacts areas such as ball in play and in game recovery. If it does, as in both codes of Rugby, start to alter the physical demands of the game, the challenge for clubs will be to adapt training, ensuring players are prepared for these new demands. 

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SSA Blog: What it takes to win a Grand Tour - or two...

Riders performances, like in any sport, consist of a number of interdependent factors. Cycling at its professional level contains some of the most elite endurance athletes in the world. To achieve this level takes enormous dedication, going through years of training to develop the endurance adaptations needed to compete within the professional peloton.

SSA Blog: Stick or Twist? When to sack a manager

Leicester City head to Anfield tonight without Claudio Ranieri for their first game since his departure. He becomes this terms fifth Premier League manager to lose his job, following a disappointing defence of last season’s incredible title win.

Ranieri’s departure has divided football. So, should Leicester have stuck by their man or were they right to recognise a performance issue that support and loyalty wasn’t going to fix?

A number of studies have examined the impact of managerial changes across professional sport. Perhaps the most comprehensive in English football was published by Audas et al, in 2002. They examined results and managerial changes from every professional game for almost 20 years. Their model was able to assess the impact of short-term changes, meaning those which occurred within the season, rather than just season to season variations. Interestingly, they found clubs who made changes mid-season actually fair worse than those that don’t.

Last season, 12 premier league managers were sacked, 9 during the season, including 3 managers of 2 eventually relegated clubs, Newcastle and Aston Villa.    

Using last season’s example it can be argued, in conflict with Audas and his team, that a managerial switch will work. Swansea, Chelsea and Sunderland were all threatened with relegation when a change was made. If the objective was to avoid relegation, then these changes have to be seen as successful, if only in the short term.

A University of Warwick analysis by Bridgewater (2009), found that managerial changes do create a short term ‘bounce’ on team results. He attributed this to players attempting to impress a new manager to secure future employment. The paper described a ‘honeymoon period’ that would last between 12 and 18 games before performance regressed to pre-change levels.

However, it’s easy to review performance after the event, drawing conclusions about long vs short term benefits. When a club is facing relegation from the increasingly lucrative Premier League as Leicester City is, is there any research to support the decision-making process?

One study which attempted to develop an evaluation model was published by Chris Hope in 2003. Hope’s study, ‘When should you sack a football manager?’ identifies three key variables a club must consider when making a decision regarding the manager’s future:-

  1. Honeymoon – the period during which the club will not consider sacking a manager
  2. Trapdoor – average number of points per game that is expected
  3. Weighting – importance of recent results versus previous performance

The author presents a mathematical model to be used in real time with the above parameters adjusted according to a club’s performance objectives. Hope acknowledged a number of limitations with his model but it marked a quality step into a multifaceted issue that any empirical evidence base would help support.

Bell et al, (2013) published ‘The performance of football managers: skill or luck?’ Building on Hope’s 2003 work, Bell’s model is a complex equation that takes into consideration performance, while also factoring the increased financial influence of the game. This ensures it doesn’t favour managers presiding over expensive squads. Their model uses the flowing six criteria:-

  1. Total player wage bill
  2. Total net transfer fund
  3. Total number of injured players
  4. Total number of suspended players
  5. Total number of unavailable players (e.g African Cup of Nations)
  6. Total number of non-Premier League games  

Leicester City increased their transfer spending and wage bill by 82% and 37% respectively on the previous season and while player availability has been reduced, the correlation (.75) between wages and points would more than compensate for this.

When we examine Leicester City’s performances this season, particularly with the weighting given to the last 5 games (as proposed by Hope, 2003), the numbers show that the decision to sack Ranieri was the correct one. According to Hope (2003), a rating below .74 points per game (when adjusted) should result in the sack. Ranieri’s rating was .66……

Those that believe Leicester City should have stuck by Ranieri are arguing for a season long ‘Honeymoon period’ following the title win. This is a reasonable position to take, particularly for a fan. But in the increasingly commercialised Premier League, the numbers justify the owners decision to let Claudio go.