Premier League: 'Expected goals' tells us whether a player really should have scored

-BBC Sport

"He's got to score from there!" "He should have had a hat-trick!" "He couldn't miss that!"

We've all said or heard these things while watching games, but is our frustration at missed opportunities justified?

Quite possibly not, according to a new method for analysing chances - "expected goals" - which is being used more and more by Premier League clubs.
Expected goals - what is it?

Did you know, only about one in every nine shots in the Premier League ends up as a goal?

And even relatively clear-cut chances are not scored as regularly as you might think.

"Expected goals" is a metric which assesses every chance, essentially answering the question of whether a player should have scored from a certain opportunity.

Put simply, it is a way of assigning a "quality" value (xG) to every attempt based on what we know about it. The higher the xG - with 1 being the maximum - the more likelihood of the opportunity being taken.

So if a chance is 0.5xG, it should be scored 50% of the time.

In the image below, Lamine Kone's effort from less than six yards out for Sunderland against Everton was 0.91xG. It was such a good chance it should be scored 91% of the time.

      Even Sunderland couldn't miss a chance as good as this one

How is it worked out?

Football data experts Opta have analysed over 300,000 shots to calculate the likelihood of an attempt being scored from a specific position on the pitch during a particular phase of play.

The factors taken into account when assessing the quality of a chance include:

• Distance from goal
• Angle of the shot
• Did the chance fall at the player's feet or was it a header?
• Was it a one on one?
• What was the assist like? (eg long ball, cross, through ball, pull-back)
• In what passage of play did it happen? (eg open play, direct free-kick, corner kick)
• Has the player just beaten an opponent?
• Is it a rebound?