Measuring The Invisible

Altan Ramadan Toffa Leave a Comment

Leicester striker Jamie Vardy is being presented with good opportunities and consistently finishing them. No surprises then that he is the EPL’s top goal scorer.

When watching football it is easy to assess performance in terms of goals, assists (the final pass before a goal) and tackles.  But the real value of a player is often the pieces of play that are not so easily noticed.

Runs off the ball, passes that create opportunities to provide a simple assist for a tap in finish, interceptions through good positioning and quick transitions to attack through one or two touches on the ball are the things that good players regularly deliver.

Unfortunately, these skills are often overlooked or not visible if the focus is purely on a goal-scoring outcome.

Revisiting Assists
An assist is only recorded when a goal is scored.  The beautifully weighted pass which splits a defence effectively never happens if the striker fails to take advantage of the opportunity.  However, in a 2 v 1 attacking situation, a five-yard pass is recorded when the finisher rolls the ball into an empty net.

Assists do not credit the inventiveness of an attacking player who is providing opportunities to a wasteful striker.

However, by tracking Expected Assists (ExpA) an attacking player is rewarded for creating chances.

An ExpA value is created based on the likelihood of a chance being scored – the distance to goal, angle, proximity of defending players and whether or not the attempt is delivered as a header or kick (the foot being more accurate).

By adding up the number of assists per match, a player is granted an ExpA value.

For professional clubs this value is becoming increasingly important and complex when assessing performance.

Yet the philosophy behind the measure is what matters from a Top Flight Football Academy perspective.  It should also matter for young attacking players when they consider how well they played in a match – how many chances did they create for teammates that were reasonable goal scoring opportunities?

Expected Goals (ExpG)
Likewise, it is useful to measure the Expected Goals (ExpG) rate of a player.

When considering efficiency in front of goal, would you prefer the striker who scores a hat-trick but misses four simple chances, or the striker who has one difficult chance in the entire match but clinically converts?

The ExpG rating is effectively the number of goals expected from a player given the number of opportunities that the player receives.

The measure is particularly useful in determining if a player (or team) is getting into the right position at the right time to score goals.  It is also hard on players that attempt high risk opportunities (e.g. shots from 30 yards).

Liverpool, for example, in its last four home games has scored just 3 goals from 75 shots.  Each of those goals was against lowly Exeter City in an FA Cup replay.  It would seem Liverpool are either not creating reasonable goal-scoring opportunities or have poor finishers (or both!).

Conversely, English Premier League leaders Leicester City became the final club in the division to score from outside the penalty area this season when Danny Drinkwater had a successful blast in their late January 3-0 victory over Stoke.

Leicester, unlike Liverpool, is creating chances that have a higher chance of conversion.  No surprises that the top goal scorer in the Premier League is the Leicester striker Jamie Vardy – he is being presented with good opportunities and consistently finishing.

What It Means
So, before determining how well a player performed in a match, it is important to consider the whole picture.  It is easy to judge a player on the obvious but more difficult to determine what they did well if it is not measured.

In a sport like football where often only goals are the yardstick of success, the player making the greatest contribution to a team may not be easily apparent.

You might be surprised at who the big contributors to team success really are – often it is not the player you think it is.

The Correspondent – Michiel de Hoog (Sports and Analytics) – “Why notorious klutz Lex Immers is actually one of the nation’s best soccer players.  Or was.”

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