One of the most talked about advanced stats in football today is expected goals. Often referred to in its shorthand abbreviation as ‘xG”, simply put expected goals is the likelihood of scoring based on where and how a shot occurs. While many guard their expected goals model with secrecy, there is a lot of great public work available on expected goals in football. The most famous of this work, is the expected goals manifesto Michael Caley wrote. Michael has been doing great work with expected goals for a long time, and I strongly suggest you give him a follow on twitter for his xG maps. With all this great public knowledge available, surely we can use it to track the progress of all the great strikers in the SPFL like Leigh Griffiths, Adam Rooney, Liam Boyce, and others, right? Erm, not quite. If you are reading this, you likely know that Scottish football is at the scrap end of the TV money table, meaning that a few selected SPFL games are on tv. With so few games on TV, anyone (like your humble author) wanting to calculate xG for the SPFL are reliant on the media to provide the data necessary to calculate it. And with the BBC and Opta teaming up to form a human ¯\_(ツ)_/¯ emoticon towards Scotland, we have to make due with what the Beeb gives us. Anyone who’s ever seen a SPFL live match report on the Beeb knows they use about six or seven descriptions to describe chances. Terms like “in the 6 yard box”, “to the right of the box”, and “outside the box” are the most that we get, the rest is left up to our imagination. Based on this, the great Ben Torvaney of Analytics FC created an “expected goals model” for the limited info we do get from the BBC (I believe the Championship in England gets the same cold shoulder live match descriptions as the SPFL). Friend of the blog, Seth Dobson of Fitba Fancy Stats has done some great work on the scoring rate of each of these locations, which I highly recommend. I have used Ben’s model to get the expected goal totals of every team and player in the SPFL and below are the top 11 (I can’t say no to you, Ali Crawford). Along with their xG totals, I have their xG compared to their actual goals, xG per 90 minutes compared to their actual goals per 90, and xG compared to the number of shots taken.
Looking at expected goals compared to goals, the likes of Adam Rooney of Aberdeen and Steven MacLean of St. Johnstone are far and ahead of their goal totals based on their expected goals for the season. Rooney got a lot of those goals at the penalty spot during Aberdeen’s eight game win streak at the beginning of the season. All but one of MacLean’s goals came from open play, though it seems that this type of performance from him seems tough to continue. Chad Murphy wrote a very interesting piece about clubs selling overachieving strikers compared to their xG totals, and after reading that piece, Rooney and MacLean’s names jumped out in my head as perfect examples of this. Neither club seems to need to sell from a financial perspective, and who knows if anyone is banging down the doors in Aberdeen or Perth to get either Rooney or MacLean, but it might be smart to sell based on the likelihood of the two not being able to sustain these results.
When we look at expected goals per 90 minutes compared to actual goals per 90 minutes, MacLean and Rooney stick out like a sore thumb again. However, if we look at the other end of the spectrum, we see a player who made headlines when he was subbed out earlier than he thought necessary. Kris Commons’ contributions to Celtic have been debated greatly since that day. He has the 2nd highest xG total in the SPFL, the 2nd highest xG per 90 minutes in the SPFL, yet only has 3 goals in league play. Taking a look at the SPFL Goals + Assists leaders, we see Commons with 5 assists in the league thus far, putting him at 0.9 Goals and Assists per 90 minutes, so Commons is definitely contributing to the Celtic attack in various ways, but should he be scoring more goals? Probably. Now please don’t throw your jacket at me, Kris.
Leigh Griffiths has been a one man (not two man, much to the chagrin of much of the Celtic support who would like to return to the days of sewn leather balls, “getting stuck in!”, and playing two strikers up top) wrecking crew. Leading the league in goals, xG, and shots, Griffiths great play has moved Celtic to the top of the league. Much has been talked about the turn around last year Griffiths made when he drove himself to a Celtic reserve match against Sunderland just to get some game time. Since that trip down South, Griffiths has been fabulous and is a definite SPFL Player of the Year candidate (and his hair should be up for Comeback Player of the Year. It took awhile but the hair transplant is finally yielding results!) While Griffiths play has been great, let me take this opportunity to confess my undying man crush for Ross County’s Liam Boyce. Could Boyce have easily been included in the group of strikers over performing that likely won’t be able to replicate that form going forward?
Yes NO! YOU SHUT YOUR DIRTY MOUTH! HE WILL ONLY BE SOLD TO REAL MADRID TO REPLACE CR9! Boyce has been a big part of Ross County’s unexpected success thus far, and while his stats don’t scream “PROBABLY A LITTLE LUCKY!” like some other SPFL strikers do, I wouldn’t be shocked to see the former Cliftonville man come back to earth. In fact, I think we have seen a little bit of that, with Boyce not scoring in his last 4 matches (though those matches included fixtures against Celtic, Hearts, and Aberdeen the top 3 clubs in the table) and only 1 shot in 3 of those 4 matches. Could clubs be focusing their defensive efforts on Boyce?