I'm not that familiar with soccer stats, but this section needs a reply:
> A “shutdown” cornerback like Richard Sherman can be a star in the NFL thanks to interceptions, broken up plays and tackles. “Lock down NBA defenders” like Bruce Bowen and Dennis Rodman can prove their worth with steals, blocks and rebounds. Football has goals and assists, that’s it.
Just as in soccer, those "counting stats" are not great measures of defensive ability. The recently retired cornerback Darrelle Revis was regarded as the best defensive player in the NFL from about 2009-2011. Yet he did not rack up interceptions or pass breakups -- in fact, in 2010, he had 0 interceptions and only 9 pass breakups over 13 games. Why? Because the receivers he was covering were never open, so quarterbacks rarely attempted to pass in his direction.
Similarly, steals, blocks, and rebounds are only a vague indicator of defensive ability; it's never a bad thing to get a steal or a block, but if you routinely leave your man to try to poke the ball away from someone else's man, you're likely hurting your team overall. The NBA has been working on developing better stats, including deflections (you get your hand on a pass but don't necessarily come away with the steal) and shots defended (you're within a short distance of a shooter). But Darryl Morey, general manager of the Houston Rockets and a well-known stats nerd, has said in a Reddit AMA that no publicly available defensive statistic is useful.
Part of this is because all three sports in question are team sports, which means a great deal depends on the defensive scheme. You may not block shots, but is it your job to block shots or to stop the ballhandler from getting near the basket? You don't get tackles, but is it your job to get tackles or to funnel the ballcarrier right into the linebackers?
It's extremely difficult for any outsider to determine the defensive effectiveness of a player. The only thing we can offer is guesswork.
Sounds very similar to the problem of accurately assessing performance of software developers working as a team.
Sure, you have people who write a ton of code and implement a lot of features, and fix a lot of bugs, who clearly are contributing a lot. But you also have people who, though other means (code reviews, refactoring and other code-health work, etc) ensure that a project is maintainable and sustainable.
How do you measure the value of 100 bugs that never made it to production because of high quality code-reviews? Or those 5 high-value features which were a snap to implement because somebody took the time to clean up all the cruft from Mr Rockstar Bro who made a gigantic mess?
You can begin to measure a player's defensive performance by working out what they allow the _opponent_ to do (or indeed not do), especially in something like soccer with larger play areas and slightly less fluidity of movement. There's a section in the Soccermatics book about an old metric I worked on called PATCH which implemented this quite naively based on defender territory and ball progression, which nevertheless flagged up people like Umtiti before his Barcelona move.
Of course there's also stuff like GoalImpact which just tries to apply plus minus to football, but all the old arguments about football being a low scoring game apply here.
> A “shutdown” cornerback like Richard Sherman can be a star in the NFL thanks to interceptions, broken up plays and tackles. “Lock down NBA defenders” like Bruce Bowen and Dennis Rodman can prove their worth with steals, blocks and rebounds. Football has goals and assists, that’s it.
Just as in soccer, those "counting stats" are not great measures of defensive ability. The recently retired cornerback Darrelle Revis was regarded as the best defensive player in the NFL from about 2009-2011. Yet he did not rack up interceptions or pass breakups -- in fact, in 2010, he had 0 interceptions and only 9 pass breakups over 13 games. Why? Because the receivers he was covering were never open, so quarterbacks rarely attempted to pass in his direction.
Similarly, steals, blocks, and rebounds are only a vague indicator of defensive ability; it's never a bad thing to get a steal or a block, but if you routinely leave your man to try to poke the ball away from someone else's man, you're likely hurting your team overall. The NBA has been working on developing better stats, including deflections (you get your hand on a pass but don't necessarily come away with the steal) and shots defended (you're within a short distance of a shooter). But Darryl Morey, general manager of the Houston Rockets and a well-known stats nerd, has said in a Reddit AMA that no publicly available defensive statistic is useful.
Part of this is because all three sports in question are team sports, which means a great deal depends on the defensive scheme. You may not block shots, but is it your job to block shots or to stop the ballhandler from getting near the basket? You don't get tackles, but is it your job to get tackles or to funnel the ballcarrier right into the linebackers?
It's extremely difficult for any outsider to determine the defensive effectiveness of a player. The only thing we can offer is guesswork.