Let’s ask the numbers. 

Damon debuted in the majors at age 21, while Ellsbury’s debut came at age 23. This alone should tell you something about the two players: better players tend to make it to the majors sooner, although there are very many exceptions. Maybe Ellsbury is an exception.

At age 21, Johnny Damon demolished double-A pitching, to the tune of .343/.434/.534. He earned a call to the majors and posted a .765 OPS in 188 at bats. Jacoby Ellsbury, at age 21, was in his last year at Oregon State, and also spent some time in short season ball with the Red Sox. 

At age 22, Damon was a full-time outfielder, hitting a paltry .271/.313/.368 with 6 homers in 145 games. At the same age, Ellsbury split time between high-A and double-A, putting together a combined line of .303/.382/.425 with seven homers in 111 games.

By age 23, Damon was showing signs of improvement, hitting .275/.338/.386 with 8 homers. Ellsbury, meanwhile, tore through double-A and triple-A (hitting .323/.387/.424 along the way), and finished the season with the Red Sox, where he hit .298/.360/.380 and played an important part in their championship season. It seems that, by age 23, Ellsbury had “caught” Damon in terms of development. Age 24 is where it gets particularly interesting. 

At 24 years old, Damon played his third straight full season (he played in 161 games), and he once again showed improvement – particularly in the power department. Damon hit .277/.339/.439 with 18 homers and 30 doubles, a huge improvement over his power numbers of the previous two seasons. Ellsbury’s age-24 season was in 2008, and he hit .280/.336/.394. Furthermore, the two players’ plate discipline was remarkably similar (as it had been in the minors, too): Damon drew walks in 8.3% of his plate appearances and struck out in 13.1%; Ellsbury walked in 6.9% and struck out in 14.4%.

After age 24, Damon transformed his game. In his age-25 season he hit .307/.377/.477 and walked 17 times more than he struck out. That began an impressive run during which his OBP was below .350 only twice through this year, and he had six seasons of at least 14 homers (not to mention at least 30 doubles in every season except 2007 and 2008).  

What does this mean for Jacoby Ellsubry? Well, from a purely statistical point of view (and I recognize that there are many other factors to take into consideration – notably, the size/strength of these two players), Damon’s age-24 season was very similar to Ellsbury’s season. The difference, of course, is the power: Damon slugged 45 points higher than Ellsbury, and walked (slightly) more while striking out (slightly) less.

While 45 points of slugging percentage may not seem like a big deal – especially for players whose games rely more on plate discipline and speed – I posit that the slugging difference between Damon and Ellsbury is hugely important.

After Damon’s age-24 season, the power that he had shown in the minors and began to show in the majors really developed. Sure, Damon was not a hulking slugger, but he could hit a lot of doubles, and could be counted on for ~15 homers a year. This is important, I believe, because it contributed to Damon’s impressive walk totals. In fact, much of Damon’s value was tied up in his consistently-high OBP, which was inflated by between 60 and 70 walks a year (seriously, check out Damon’s walk totals: he had between 60 and 70 walks in every year from his age-25 season through now, except for two: 76 walks in 2004 and 53 in 2005). 

While Damon did not draw a ton of walks, I believe the vague threat of Damon’s power allowed him to garner as many walks as he did. While Damon wasn’t a threat to hit a bomb every night, pitchers couldn’t challenge him with a fastball down the middle.

Ellsbury, on the other hand, may never develop that kind of power. And if he doesn’t, Ellsbury’s plate discipline numbers could suffer – and, along with it, his OBP. One need only look at the progression of Ellsbury’s season: in the first three months, he struck out 40 times and drew 30 walks – roughly a Johnny Damon type season in those categories. However, Ellsbury was slugging only .383, and it became evident that he didn’t handle good fastballs well. As a result, teams began challenging him more often. 

In the final three months of the season, he also struck out 40 times, but only drew 11 walks. Teams decided to go right after him, and while Ellsbury’s strikeout rate didn’t rise, but he drew walks at only 1/3 of the pace as before.

Ellsbury is still only 24, and thus has room for improvement. The problem for him is that he’s never shown the ability to hit for power in his entire career. Aside from 17 games as a 23-year-old in double-A, he’s never slugged above .434 at any minor league level. He’s not a big guy, and scouts have never seen him as someone who would develop power as he got older.

It seems fair to say that Jacoby Ellsbury is a lot like Johnny Damon Lite. Unfortunately for Ellsbury, if this really is the case, then he won’t be able to post the OBPs that Damon posted. Damon’s power was a key to his value, not only because of the inherent value of his power, but also because it likely instilled a necessary amount of fear to allow him to draw a walk and keep his OBP high. As of now, Ellsbury lacks this intimidation. 

Ellsbury has one thing going for him that Damon didn’t: namely, his baserunning ability. Ellsbury has always been an excellent base stealer (although he showed drastic splits in this too: in the first three months, he stole 34 bases in 38 attempts; in the last three months he stole 16 bases in 23 attempts).

2009 will be an extremely important season for Jacoby Ellsbury. Was his poor second half baserunning and walk rate a product of fluctuation/bad luck/Ellsbury getting worn down/pitchers making adjustments? If so, Ellsbury will have to make adjustments and will likely improve. However, if his poor second half was a result of Ellsbury’s lack of talent finally catching him with him, he may never develop into more of a fringe-starter type of player.