WHILE securing Celtic's first trophy under Ange Postecoglou and Kyogo Furuhashi’s tremendous goals were the obvious high points coming out of Sunday’s League Cup triumph, it did not come without a ‘cost.’
David Turnbull’s injury will thin an already threadbare squad, with central midfield having been a specific area of concern for the entirety of this season to date. With four huge games prior to the winter break, what will be the implications on performance levels?
Turnbull’s value so far this season has arguably been underappreciated. Here are comparisons with Callum McGregor and Tom Rogic in domestic games so far this season:
We can see from these radars that Turnbull has provided the highest amount of overall OBV of the three, with his pass OBV of particular note at more than double the other two.
Next, let us look at passing and creativity-related metrics to try to ascertain from where the differences in OBV may be arising:
Two major issues which jump out in those two radars are the importance of Turnbull’s role as primary set-piece taker, as well as his relative value versus McGregor when it comes to shooting.
First, some perspective on his value as set-piece taker. He is currently first in the league in xG from set-pieces at 0.19 per 90 minutes, with Calvin Ramsey of Aberdeen second at 0.18, then James Tavernier third at 0.13. Fourth is Scott Tanser of St. Mirren, who is all the way down at 0.09.
Quality versus quantity is also an obvious factor: Turnbull’s average xG assisted per key pass from set-pieces has been 0.09 on 2.08 key passes, versus 0.07 for Ramsey on 2.43 and 0.06 for Tavernier on 2.10.
Turnbull also averaged about 0.09 in his one full season at Motherwell in 2018-2019, so this level of quality is not a new development. For further perspective, McGregor was the most often used set-piece taker in league games for the 2018-2019 season, where he averaged comparable to Tavernier at 0.06.
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Another aspect of Turnbull’s value appears to be tied to his ability to retain possession in build-up and accurately progress the ball by breaking opponents’ lines. Per Wyscout, Turnbull has averaged 8.37 progressive passes per 90 minutes in league games this season, while being accurate on 89.17 per cent. By comparison, McGregor has averaged 8.64 while accurate on 79.02 per cent, with Rogic at 6.49 and 76.92 per cent.
With McGregor likely moving forward to replace Turnbull, this ensemble of metrics has me a bit concerned with his ability to offer comparable output from open play – particularly as relates to shooting. Also, whoever ends up taking set-pieces is unlikely to be of comparable quality, so the net impact is likely negative.
However, the shift of McGregor as the left-sided attacking eight will not be the only likely change in the four upcoming games. Assuming he is and remains fit, Nir Bitton appears the likely choice at defensive midfielder. How has he measured up?
Here is Bitton’s OBV radar compared with McGregor's so far this season, and then also versus the very small sample size of minutes James McCarthy (presumably next in line for the position) has played:
We can see that with the exception of his shot OBV (please stop shooting, Nir!) he’s offered comparable value to McGregor this season, and has dwarfed McCarthy. His pass OBV stands out relative to the other two, which is anecdotally supported by his seeming initiative to attempt line-splitting passes.
For additional context, here is Bitton so far this season compared to Scott Brown in his 2018-2019 season at Celtic:
Once again, we see the huge disparity in Pass OBV, and how superior his OBV would have been with better shooting decisions (please stop shooting Nir!), including comparable defensive value.
David Turnbull’s production will probably not be easy to replace, though McGregor is likely to offer comparable value relative to ball progression and creativity from open play.
Bitton appears to offer comparable value to McGregor in the defensive midfield role, so overall the changes look like they may be a marginal negative.
If one of Bitton, McGregor, or Rogic miss meaningful time over the next four games? Better spike that eggnog.
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