Michael Bourn’s Questionable Future Defensive Value

Michael Bourn is a pretty terrific defensive center fielder. Last year, he was the best defensive outfielder in baseball by UZR (after you account for the positional differences), grading out as 25 runs above an average defensive player, and it wasn’t a one year aberration, as no player has a higher FLD+POS rating over the last four years either. With over 6,500 innings big league innings, we’re not dealing with problematic small samples either. Bourn has been a tremendous defensive asset this far in his career.

However, teams are no longer as willing to pay for past performance as they used to be, as front offices are now populated with people who are more interested in projecting a player’s future than they are with paying for an established track record. So, while Bourn’s defensive performances are notable, they’re only worth paying for to the extent that they inform our understanding about what they mean for his defensive value in the future. Now 30-years-old, Bourn’s getting further and further from his peak, and defensive skills seem to plateau earlier than offensive skills, so there’s some legitimate questions about just how much of his defensive value he will retain in future years.

To try and shed a light on that question, we can identify players who were valuable defensive outfielders in their twenties, and then see how much of that value carried over to their thirties. If you’re Michael Bourn, or Michael Bourn’s agent, you might want to stop reading now, because the answer probably isn’t something you’re going to want to hear.

I started off by filtering the leaderboards to display outfielders from 18 to 29 years of age, and then limited the list to just those who received at least 2,500 plate appearances from 2002-2011. This gave us a list of 44 outfielders who got regular playing time in their twenties during the UZR era, and also had a chance to have an age 30 or older season in 2012. There were 44 such players, and of those 44, 12 of them averaged +5 runs or better (by UZR plus the positional adjustment) per 600 plate appearances during that time. For ease of conversation, we’ll just call FLD+POS per 600 “defense”, and it will be labeled as DEF in the table below.

Of those 12 players, three of them don’t provide us with any useful information about their age 30 and beyond seasons. Bourn hasn’t played in his thirties yet, Willy Taveras was out of baseball after age 28, and Carl Crawford only managed 125 plate appearances in his age-30 season last year. That leaves us with nine outfielders who were regularly valuable defenders in their twenties and have already amassed at least a bit of playing time in their thirties. Below, we present a table of those nine outfielders, their average seasonal defensive value through age 29, and then their seasonal defensive value from 30 and beyond.

Name	29- PA	29- DEF	30+ PA	30+ DEF	Change
Andruw Jones	3,305	19.7	2,047	4.9	(14.8)
Aaron Rowand	2,804	11.5	1,865	3.9	(7.6)
Coco Crisp	3,451	11.0	1,419	1.7	(9.2)
Corey Patterson	3,569	9.2	738	(4.5)	(13.7)
Juan Pierre	4,333	6.8	2,715	(5.1)	(11.9)
Curtis Granderson	3,424	6.3	1,375	(8.0)	(14.4)
Shane Victorino	3,043	6.1	1,252	4.7	(1.3)
Carlos Beltran	3,299	5.9	3,171	(0.7)	(6.6)
Alex Rios	4,125	5.3	1,210	(5.8)	(11.1)
—	—	—	—	—
Average	3,484	9.1	1,755	(1.0)	(10.1)

That right hand column tells the story, with all nine players posting worse defensive numbers from 30 on than they did through age 29, and most of them declining in really large ways. Andruw Jones went from best-of-all-time to okay. Aaron Rowand and Coco Crisp went from great to slightly above average. Corey Patterson, Juan Pierre, Curtis Granderson, and Alex Rios went from comfortably above average to well below average. Only Shane Victorino hasn’t taken a huge step backwards, but he’s only played two seasons in his thirties, so he has both a smaller sample size and his data skews towards his younger years. Overall, the group average very nearly matches Bourn’s personal mark (9.1 versus 8.9), and the group as a whole was rated slightly below average defensively in their thirties. Not a great sign for Bourn’s long term future.

Of course, no team is going to sign Michael Bourn through his age 39 season, so casting that large of a net forces us to include some seasons that we shouldn’t necessarily care about when discussing his next contract. Realistically, he’s not going to get more than a four year deal at this point, and even that might be pushing it. So, let’s re-run the table, only looking at these players from their 30-33 seasons:

Name	29- PA	29- DEF	30-33 PA	30-33 DEF	Change
Andruw Jones	3,305	19.7	1,556	7.3	(12.4)
Aaron Rowand	2,804	11.5	1,865	3.9	(7.6)
Coco Crisp	3,451	11.0	1,419	1.7	(9.2)
Corey Patterson	3,569	9.2	738	(4.5)	(13.7)
Juan Pierre	4,333	6.8	2,276	(5.0)	(11.7)
Curtis Granderson	3,424	6.3	1,375	(8.0)	(14.4)
Shane Victorino	3,043	6.1	1,252	4.7	(1.3)
Carlos Beltran	3,299	5.9	1,954	4.6	(1.2)
Alex Rios	4,125	5.3	1,210	(5.8)	(11.1)
—	—	—	—	—
Average	3,484	9.1	1,516	(0.1)	(9.2)

Unfortunately for Bourn, the numbers don’t really improve much. Jones and Beltran get slight bumps, since we’re dropping off their later seasons where their defense really declined, but for most of these players, we were already looking at the beginning of their thirties. Granderson is only 31, like Victorino, and he’s already experienced a big dropoff according to UZR. Same with Rios. Crisp is just 32, but hasn’t graded out nearly as well as he did in his twenties.

Part of this is just natural regression to the mean. We started by selecting players at the very top of the scale, so no matter what metric we were measuring, we would have expected future performance to be worse. And, yes, we are dealing with some sample size issues on for 30+ years, as the nine players combined for 31,000 plate appearances in their twenties but just 13,000 in their thirties. Crisp, Rios, Victorino, and Granderson could all post monster defensive numbers in 2013, which would significantly alter the numbers if we re-ran the table 12 months from now.

But, the fact remains that Major League teams have seen the most recent crop of great defensive outfielders age very poorly, at least when it comes to maintaining their defensive value past their age-30 season. With so many examples fresh in their mind, it shouldn’t be hugely surprising that teams aren’t overly eager to pay a premium for Bourn’s decline years. He’s starting from a higher baseline than most of these guys, and he’s certainly a better hitter than Patterson or Pierre, but if Bourn follows the pattern and regresses into something like an average defensive outfielder over the next few years, he’s not going to be a particularly great player anymore. He won’t be useless, but he needs to maintain a decent chunk of his fielding ratings in order to remain a strong asset in his thirties. Recent history suggests that teams have been wise to proceed with caution.