Goals and assists are terrible measures of success. There is no record of the difference between a tap-in and a 20-yard side volley once the ball's in the net. A single pass difference separates an assist from any other pass, no matter its location, difficulty, or importance. Nevertheless, goals and assists are the numbers we measure that contribute most reliably to immediate success or failure. The further a player is removed either from scoring a goal on the offensive end or conceding on the other, the harder it is to statistically define success.
So... if a defensive midfielder's performance deteriorated over time, how could you tell?
Scan the comments at SaH and you'll find some that question whether Osvaldo Alonso's play has dropped in the past couple years. Some reduced performance should probably be expected in the Honey Badger's 2015 numbers simply due to his persistent injury problems. Seven different Sounders have collected at least 1 start in central midfield or defensive midfield this season, including the newly available Brad Evans - should we begin to question Alonso's spot once healthy?
|Passes per 90'||61.02||65.34||66.44|
|Pass Share (%)||15.15||14.32||14.14|
|Pass Accuracy (%)||88.22||91.01||91.57|
|Def. Actions per 90'||10.55||10.90||9.79|
|Defense Share (%)||13.07||13.39||13.51|
|Tackle Success (%)||79.39||74.42||76.19|
|Lost Possession per 90'||9.68||8.74||7.29|
|Chances Created per 90'||2.01||1.67||0.95|
There is, in fact, little evidence for significant decline in Alonso's play. His defensive rate stats are down slightly, but his share of overall team defense has risen. Ozzie's chances created (key passes + assist + shots) have fallen off, but his chances have rarely been dangerous in the past (leaving the final pass or shot to another player could even be a somewhat positive development). The numbers tell us that Alonso remains quite able to take a large defensive responsibility and perform quite well as a holding midfielder. If he's had any greater difficulty in those aspects of his play, it has been statistically overwhelmed by the sheer number of positive or mundane actions he takes in every game... but we should remember he is not a creator.
Is there a better way to measure the performance of a strictly defensive player?
When an opponent employs a creative central attacking midfielder, their performance could stand as a proxy for the defensive midfield (we looked at centerbacks through changes in opposing forward success in a similar fashion). The graph above compares the performance in chance creation and possession loss of Orlando City's Kaká in each of his 23 games of 2015 against his full season average (a negative value indicates fewer chances and more turnovers on their respective axes). When Kaká fails to create up to his usual standards, he often at least contributes to solid possession befitting his pedigree (the r-squared of the above linear regression is 0.11). Sunday's game is one of only a handful of exceptions, below average in both metrics (and one might also say that his two chances - one shot and one key pass - were not particularly threatening). The central midfield pair of Evans and Eric Friberg played a significant role in holding him to one of his worst games in the league.
The role chart above depicts the pass and defense share of each Sounder receiving starts at CM or DM in 2015 (admittedly, Cristian Roldan at 1 start, Evans at 2, and Friberg at 4 have fairly dubious sample sizes). Seattle's CM pairing has relatively large responsibilities for both distribution and defensive actions - more so this year than last - and the roles become still more demanding with the absences of Marco Pappa, Clint Dempsey, and Obafemi Martins. Roldan and Andy Rose haven't had many chances to work in Sigi Schmid's favored 4-4-2 with Alonso, but their inability (so far) to scale up their activity shares to the starters' level may be an important reason. Pineda's lesser defensive share reflects the greater creativity expected of his role, but he continues to struggle meeting that demand:
Friberg's ~4 chances created per 90' might not be sustained against stronger defenses than Orlando, but even diminished would fill in a gap in Seattle's 2015 offense. A heavy passing share with an attacking posture (and corresponding possession loss) requires some measure of key pass and assist reward, even given the limitations of those stats. Friberg's 2 assists - 1 each in the last 2 games - are the second and third assists from a Seattle CM this year. On Sunday, the Evans/Friberg partnership silenced Kaká while turning in the best offensive performance from the middle we've seen in quite some time. Alonso, when healthy, may fit into a similar tactical picture, but not in place of Friberg... unless the team chooses to shore up the defense to the detriment of the attack.
Raw data for this work was collected from OPTA via whoscored.com.