21 November 2014

Can We Trust Lough's Defense?

Before David Lough went on his hot offensive streak in the middle of last season, Jon made the argument that Lough is actually a starter in disguise due to his excellent defense. He noted that Lough’s defense has been consistent for each season and projects to make him nearly a 2 WAR player over a full season. Pat suggested yesterday that an outfield consisting primarily of Adam Jones, Steve Pearce, Alejandro De Aza, and Lough could be acceptable. Certainly understanding Lough's value would be helpful. The main question is whether or not one can believe that Lough's defense is as valuable as UZR suggests.

Jon also noted in his earlier article that Lough’s defense may have been consistent for each season but that he’s played a limited number of innings in the field. So I looked at all outfielders that played at least 500 innings in the outfield from 2012-2014, and saw some surprising players in the top 20 in total UZR. For example, Lough’s total UZR was good for 11th out of 193 outfielders despite ranking 117th in innings. Lorenzo Cain and Juan Lagares were in the top five in total UZR despite ranking 58th and 87th in innings. Craig Gentry ranked seventh despite playing 12 more innings than Lagares. Dyson ranked ninth playing only 113 more innings than Lagares. This trend continues for outfielders that played 500 or more innings in the outfield from 2010-2012. Gardner ranked #1 in UZR and 59th out of 183 in innings. Peter Bourjos ranked #2 in UZR and 70th in innings. If outfielders with a minimal amount of innings playing in the outfield (i.e small sample sizes) have some of the highest UZRs then is there a correlation between innings played on defense and UZR? If not, then it may not make sense to say that an outfielders defensive value will improve if he plays more innings.

In the same vein, it seems reasonable to presume that players with more plate appearances produce more runs than those with fewer plate appearances because teams are far more likely to demote a player that is struggling offensively than one that is not struggling offensively. In other words, there should be correlation between plate appearances and total offensive production.

It's possible to answer this question. For each player from 2002-2014, I downloaded the number of innings they played at each position, their UZR at each position, their total number of plate appearances, and their “batting” score as derived by Fangraphs. Fangraphs "batting" score attempts to quantify the value of an offensive player by determine the number of runs above average his offensive production was worth in a given season. Then, I did a correlation analysis between innings and UZR as well as between plate appearances and “batting”. If there is a relationship between innings and UZR then I would expect to see a moderate correlation between these variables and a similar correlation between those statistics and the correlation between plate appearance and “batting.” Here's a table with the results.

The results suggest that the average correlation between innings and UZR is about .077. Defense intensive positions such as second base, third base, shortstop, and center field have larger albeit still low correlations than those for positions like first base, left field, and right field. The results for the correlation between PAs and "batting" tell a different story.

The average correlation between PAs and “batting” was .376. The largest correlations were at offensive positions such as first base, left field, and right field while there was practically no correlation at shortstop. It should come as no surprise that teams don't give shortstops playing time based on their ability to hit.

These results suggest that there is correlation between offensive production and plate appearances but not between UZR and innings played in the field and therefore it doesn’t make sense to give a player credit for a high defensive score that occurs in only part of a season. This explains why outfielders  that only play a limited number of innings consistently have some of the highest UZRs.

There is another possible way to interpret these results. These results could mean that managers don’t value UZR highly while valuing offensive production. If this is the case then there should be a similar correlation between innings and the absolute value of UZR as well as plate appearances and the absolute value of the “batting” statistic.

The average correlation between innings and the absolute value of UZR is .65 while the average correlation between plate appearances and the absolute value of “batting” is .52. This suggests that there is a moderate to high correlation between innings and UZR. It’s just that players that play a lot of innings at a position have a high absolute value that is either positive or negative. In other words, managers care less about whether their players have a low UZR than they do about whether their player is producing offensively. If UZR does measure defense accurately then this suggests that managers don’t value defense as highly as offense especially at offense-oriented positions.

This test is inconclusive in determining whether one should feel comfortable projecting Lough to be an excellent defender based on his UZR and performance in a limited sample. This should make us pause before overly valuing a limited period of good defense. Indeed, players like Nyjer Morgan, Ryan Sweeney, Andrew Torres, Tony Gwynn Jr., Gerardo Parra, and Ben Revere are all guys that put up strong defensive numbers in a limited amount of innings and then came crashing back to earth, and Lough could follow the same path.

This suggests one of two things. Either teams have better defensive metrics than UZR and therefore don't give its ratings high credence or that teams simply value offense more than defense especially for corner outfielders. This second scenario is probably bad news for outfielders like Jason Heyward. If UZR isn't a good defensive metric then it's likely that Lough's value is highly exaggerated. If UZR is a good defensive metric then finding a corner outfielder with good defense is an easy and undervalued way to improve. If so then even if the Orioles don't trust Lough's defense they should consider finding a proven player with similar strengths.

Photo via Keith Allison


Philip said...

At least on my phone, your worksheets were blank.
It is worth mentioning that all the outfielders you mentioned are outstanding defenders. Even if UZR is a flawed stat in detail, players it identifies as being good seem to be genuinely good.
Meanwhile, the Reds are supposedly blowing up the team. How do you feel about Bruce?
Regarding Lough, the eye test tells me he has excellent range and very good hands.
I have rarely seen an outfielder as good as he is.
It is curious that no one mentions his bad baserunning, doubly surprising because of his amazing speed.
I would very much like to keep him and De Aza as well, but I'd also like to trade for someone like Jay Bruce or the National's Souza.

Matt Perez said...

Thanks for letting me know that the worksheets don't work via phone. They're fine on my computer and that means I need to find a different method.

Without open-source defensive metrics it's difficult to determine the accuracy of UZR. I personally suspect that UZRs results are plausible and that therefore defense is the new moneyball. But I can't prove anything yet. I agree that Lough passes the eye test and wonder if the Orioles feel the same way. I just wonder how much the eye test counts for.

I expect Bruce to bounce back but he's going to receive $25.5M over the next two years. He's probably worth something like $30 or $35 million. If the Reds are willing to either eat some cash or take a B- prospect in return then he makes sense. Otherwise, I don't see a fit. Bruce struggles against left handed pitching and doesn't make sense on a team with De Aza and Lough.

I'm not a big fan of players that don't make it to the majors until they're 25. Historically, a guy like Souza has about a 1 in 20 chance of being successful. It's better than zero I guess, but...