With half of the SPFL Premiership fixtures for Saturday cancelled due to inclement weather and no way for your average Scottish Football loving American to watch the matches that were not cancelled (seriously, SPFL I will give you around $20 United States Dollars a month to watch any match from the weekend online. Heck, I would even watch it tape delayed!), I turned to twitter to see what was going on in the three matches that were being played. Upon checking twitter, I saw this tweet describing the first goal in the Saint Johnstone-Ross County match. IMG_1187

You can commend David Wotherspoon for pressuring the keeper into forcing this mistake, but I think most would agree there was a bit of luck for Saint Johnstone to get a goal in this situation (to be fair to Wotherspoon, he scored later in the first half from an absolute rocket of a goal).  I had briefly discussed Saint Johnstone’s success despite low shot totals, TSR and TSoR, but the Saints match with Ross County, including their fortunate first goal, prompted me to look at PDO in the SPFL this season.

For lack of a better word, PDO measures luck (though some have a problem with that word). We discussed Dundee United’s lack of luck in relation to PDO, but as a refresher PDO is used to explain how a team performed historically, since if a team is scoring a lot of their chances and not allowing goals in the chances they allow, they are probably doing well. It measures a team’s efficiency. The formula for PDO is ( (Goals For / Shots For) + ( 1 – (Goals Against / Shots Against) ) ) * 1000. Looking at PDO and graphing it with xG we can see “lucky” and “unlucky” teams in the SPFL this season.

PDO-xG -Luck-

In the top right quadrant, we can see “Good and Lucky” teams, or teams with high PDO and high xG so far this season. Among these teams, it is no surprise we see the top four teams of the SPFL Premiership in Celtic, Hearts, Aberdeen, and Saint Johnstone. Celtic, unsurprisingly, have a high Expected Goal total and a good PDO. Aberdeen and Hearts have solid, though not spectacular numbers in both categories to back up their position on the table. Then we come to Saint Johnstone. The Saints are on the “Good and Lucky” side, but are awfully close to the top left quadrant of “Bad and Lucky”. Saint Johnstone’s PDO is a sky high 1102 on the back of their ability to seemingly score goals despite not having a high amount of shots. Their high PDO combined with their lower xG total points to a West Ham in the EPL this season type rise in the standings that might not be sustainable all season. Then again, this has been said about the Perth club for awhile now and they continue to churn out top 6 finishes in the SPFL.

In the bottom right corner we see Ross County as the lone occupants of the “Good and Unlucky” quadrant. County’s xG output suggests the Highland club should be scoring more goals, but their sun-1000 PDO hints at some bad luck for the Staggies. With the club in a top six position when few predicted such a strong start, could they dream of a possible European spot finish if the bounces start going their way, like their Highland rivals Inverness Caledonian Thistle enjoyed last season?

Speaking of Caley, Inverness Caley Thistle are the lone occupants of the “Bad and Lucky” quadrant, though they are not far off from joining the “Bad and Unlucky” quadrant. In that quadrant we see the previously mentioned Dundee United, who are on their own island in the sea of awful numbers.  Closer together in the “Bad and Unlucky” quadrant are fellow relegation worriers Kilmarnock, Motherwell, and Partick Thistle. In addition to the clubs who might have to start worry about that relegation playoff, we see Hamilton and Dundee who sit in the table 5th and 7th respectively. These clubs being near the top half of table might suggest that the talent level gap between teams fighting relegation and finishing in the top six on the table is not that great.

PDO-xPDO

Here we see the SPFL Premiership Clubs PDO compared to their xPDO. Again, in the Dundee United focused post we discussed the idea of xPDO brought up by the great Dutch football blog 11tegen11, but to refresh, normal PDO is calculated using shooting and saving percentages while expected PDO is calculated with xG per shot created and xG per shot conceded (formula: xPDO=( (xG For / Shots For) + ( 1 – (xG Against / Shots Against) ) ) * 1000)). Saint Johnstone stick out again with this graph with a high PDO, but their expected goals totals is not as high with the quality of their chances not backing up their high goal scoring. This is another sign that we might see some regression by Saint Johnstone in the table. Then again, they could continue to flick analytics in the eye.

 

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2 thoughts on “PDO and Luck in the SPFL

  1. Pingback: The Backpass Rule

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