NERD CORNER: xGas 0-2 Posh

NERD CORNER

Afternoon & welcome to the first of a new blog series for GasCast, Nerd Corner – where each week, I’ll go hardcore football geek by delving into the most hipster of stats from the Gas’ latest game.

So if you’re all in on xG, xPts and a few other things beginning with an x, read on! On the other hand, if the mere mention of such modern football nonsense is enough to make your blood boil, please feel free to roll your eyes, tut loudly & return to the previous page.

There are three certainties in life: death, taxes & middle-aged men disliking xG

UNKNOWN

What is xG? (Skip if you already know!)

For how it will be used in this & all future Nerd Corner entries, xG (Expected Goals) is simply the amount of goals that Rovers (and their opposition) would be expected to score given the chances they had in the game. It helps to give a summary of a team’s performance beyond the actual result.

xG models use various factors to assign each chance created in a game with an xG value – such as:

  • Shot location = a shot taken centrally will be rated higher – i.e. is a better chance – than one from an acute angle (assuming we are comparing like-for-like chances).
  • Shot type = an attempt with the foot will be rated higher than a header (assuming we are comparing like-for-like chances).
  • Assist type = an attempt taken from a pull back from the byline will generally be rated higher than one from a long, floated ball (for example).
  • Defensive pressure = a shot taken from a player with space & time will have a higher rating than one from a player being closely marked or challenged.
  • Goalkeeper position = a shot taken from an angle with the goalkeeper set & ready at the near post will have a lower rating than if the keeper were on the floor having just flapped at a cross (*cough* Will Puddy).

…and so on.

xG models also tend to use the same four phrases to categorise each shot taken during a game: Attempt, Half chance, Good chance & Big chance. Here’s what these phrases equate to:

  • Attempt (0.01 – 0.09 xG) = Attempts are those shots deemed to have the lowest chance of going in – usually strikes from 25+ yards. To put it another way, shots which (on average) would have a 1-9% chance of finding the net.
  • Half chance (0.09 – 0.14 xG) = Shots with a 9-14% chance of going in. Often shots from good areas but with high defensive pressure/on their weaker foot/from a tricky assist etc.
  • Good chance (0.15 – 0.23 xG) = Shots with a 15-23% chance of going in.
  • Big chance (0.24+ xG) = Shots with a 24%+ chance of going in. Big chances aren’t always a ‘sitter’ (those are probably in the 0.85 xG region), but they are chances which should be converted at least 1/4 of the time.
  • Penalties (0.76 xG) = Penalties are always given an xG rating of 0.76, as the average conversion rate of a penalty is 76% (DC’s 2015 Wembley warriors laugh in the face of this stat).

And one final bit of terminology to clear up before we take a look at this week’s game – xPts (Expected points) = the amount of points Rovers (and their opposition) would be expected to achieve based on the chances they created, if the match were replayed 10,000 times.

If I’ve lost you by this point, hopefully all will become clearer once we take a look at how Rovers fared in the wondrous world of xG during their 2-0 defeat to Peterborough United. Let’s begin!


ROVERS 0 – 2 POSH [Memorial Stadium – 03/11/20]

2nd minute / 0-0 / Sam Nicholson / Big chance (0.24 xG)

OUTCOME: Saved by keeper at near post

5th minute / 0-0 / Siriki Dembele / Big chance (0.37 xG)

OUTCOME: Scuffed across penalty area

14th minute / 0-0 / Sam Nicholson / Half chance (0.14 xG)

OUTCOME: Headed wide under pressure from keeper

31st minute / 0-0 / Sammy Szmodics / Good chance (0.15 xG)

OUTCOME: Deflected wide of far post for Posh corner

42nd minute / 0-0 / Jack Taylor GOOOAL / Attempt (0.06 xG)

OUTCOME: Screamer into top corner (ffs)

—– Half TimeROVERS (0.48) 0 – 1 POSH (0.69) —–

64th minute / 0-1 / Dan Butler GOOOAL / Attempt (0.02 xG)

OUTCOME: Screamer into top corner (ffs x2)

71st minute / 0-2 / Brandon Hanlan / Good chance (0.16 xG)

OUTCOME: Saved by feet of the keeper

92nd minute / 0-2 / Brandon Hanlan / Attempt (0.05 xG)

OUTCOME: Scuffed wide of the left-hand post

—– Full TimeROVERS 0 – 2 POSH —–

xG = 0.72 v 0.94 / xPts = 1.126 v 1.522

[NOTE: Not all attempts have been shown above, which is why the xG numbers for both sides at half & full time are slightly higher than the shots pictured add up to. Rovers had five attempts worth a total of 0.17 xG, whilst Posh had ten attempts worth a total of 0.34 xG.


Conclusions

  • A fairly even first match in terms of chances – both teams failed to take early big chances & Nicholson will maybe feel he should have taken one of his in the first half.
  • Posh’s two goals were world-class strikes with a 6% & 2% chance of going in respectively. Although the closing down could have been better… (or, you know, happened at all…)
  • Hanlan’s 0.16 xG effort was by far the best chance for either side in the second half. Posh’s highest-rated second half shot was a 0.06 xG Szmodics attempt in the 80th minute.
  • Rovers only mustered Hanlan’s 92nd minute 0.05 xG shot between the 71st minute & full time – the Gas’ worst period of the match for chance creation.

So there we have it Gasheads – many thanks for reading! (and if you enjoyed this then please do let me know as it was an absolute ball ache to put together)

UTG

{All stats taken from xgstats.com}