Who’s burning up the minors in the second half?

Split-season statistics can be misleading. It seems that major league players need only two bad Aprils in row to earn a reputation as a “slow starter” in some circles. In most of these cases, fans and analysts downplay the role random variation might have in explaining why a player might start strong or finish weakly two or three years in a row.

The minor leagues are designed to be educational, however, so split-season statistics among young minor leaguers might be a leading indicator of development. For example, current Rookie of the Year candidate Ryan Braun was among the top second-half performers after a modest first half performance in 2006.

Analysis of split seasons doesn’t always have predictive value for developing ballplayers, of course. I recently predicted a breakout season for Van Pope partly because of his strong second-half performance in 2006. While Pope is better than his .221 average might lead you to believe, he still isn’t having anything resembling a breakout season this year.

With that caveat in mind, it can still be fun to look at the top performers and speculate on what this means for their future. I will list the top 15 second-half performances in the minor leagues by players under 24 and rank them by wOBA. This statistic, featured prominently in The Book, is a run value estimate that is scaled to look like on-base percentage. Strikeout percentsage, walk percentage and isolated power (slugging-batting average) are also listed for each hitter:

Top Under-24 Minor Leaguers Since June 15
Org Name               Age    Level   PA     K%   BB%  ISOP  wOBA
TEX Chris Davis         21    A+/AA  221  26.2%  7.2%  .373  .474
TB  Ryan Royster        21        A  226  25.7%  7.1%  .314  .453
TEX John Mayberry       23    A+/AA  199  23.6%  6.0%  .269  .435
TEX Mauro Gomez         22        A  218  22.9%  4.1%  .277  .435
CLE Matt Whitney        23     A/A+  217  21.1%  8.3%  .255  .431
CLE Josh Rodriguez      22       A+  239  18.4%  8.8%  .231  .421
LA  Lucas May           22       A+  213  23.0%  4.2%  .221  .421
WAS Francisco Plasencia 23     A/A+  232  18.5% 10.8%  .244  .420
CIN Jay Bruce           20 A+/AA/AAA 231  25.1%  8.7%  .271  .420
SD  Matt Antonelli      23    A+/AA  244  14.3% 13.9%  .226  .418
COL Chris Nelson        21       A+  255  12.9% 11.8%  .277  .410
BOS Jon Still           22       A+  248  15.7% 23.0%  .250  .407  
CHC Brian Dopirak       23       A+  219  22.8%  8.2%  .229  .406
LA  Anthony Hatch       23       A+  207  16.4%  5.3%  .226  .406
BOS Jed Lowrie          23   AA/AAA  266  17.7% 10.2%  .252  .401

Here are notes on some of these prospects:

Chris Davis

Texas Rangers | 3B | 22 years old
The bad news is that Davis’ all-or-nothing approach prevents him from becoming an above-average on-base threat. Also, much of his power occurred at his hitter-friendly Bakersfield of the California League. On the other hand, he is hitting everywhere. Davis already has slugged eight home runs since a promotion to Double-A Frisco earlier this month. Perhaps most importantly, Davis’ breakout season has occurred while he moved across the infield from first base to third base. That kind of flexibility should keep him from stalling at Triple-A for the next few years.

John Mayberry

Texas Rangers | RF | 23 years old
The Rangers’ patience with Mayberry is finally starting to pay off. He isn’t a well-rounded hitter yet, but he also isn’t striking out any more often than he was at a lower level last year and his raw power has translated to 30 home runs this year.

Matt Whitney

Cleveland Indians | 1B | 23 years old
The highly-touted prospect from the 2002 draft class has survived a series of surgeries since breaking his leg in the spring following his professional debut. He was finally healthy enough to play third base in the Carolina League last year, when he demonstrated modest power while striking out in one of every three plate appearances. He began 2007 in Single-A, earned a promotion in June, and has continued to hit the ball hard all year. His discipline has worsened throughout the year and he is striking out four times for every walk he has earned in August. Whiteney has also moved into a first base/designated hitter role, so he’ll need to keep up this pace to contend for a major league role in another year or two.

Josh Rodriguez

Cleveland Indians | SS | 22 years old
Rodriguez was considered among the top NCAA infield prospects just a few years ago, but his professional career had been modest until a few months ago. Rodriguez had the worst first half among all the players in this list, so the jump in performance from April to August might be the most extreme among all prospects in baseball this year.

Jay Bruce

Cincinnati Reds | OF | 20 years old
Not much to say here. He’s probably the best prospect still playing in the minor leagues. I do worry that, as I predicted with Alex Gordon last year, Bruce won’t have the smoothest transition to the major leagues next year due to his inconsistent ability to make contact.

Matt Antonelli

San Diego Padres | 2B | 22 years old
Antonelli earned a $1.5M bonus last year because of his exceptional athelticism and polished plate approach, but his power potential was unknown. The 22-year-old transitioned from third base to second base this year and, along the way, he learned to load his hands and hit for some power. The following chart plots 15-day averages in isolated power over the course of Antonelli’s career:

Antonelli would be a solid prospect at third base. At second base, he’s a great one.

Chris Nelson

Colorado Rockies | SS | 21 years old
The ninth overall pick of the 2004 draft continues to develop slowly into the player the Rockies imagined he would be. Nelson made some notable improvements in the first half of the 2007 season when he walked and made contact more often than ever before. In July, he slugged nine home runs. Before then, Nelson had never hit more than three in a month.

Jon Still

Boston Red Sox | 1B | 22 years old
That’s not a typo in the table above; Jon Still really has walked in 23% of his plate appearances since mid-June. Among full-time minor leaguers, only Taylor Teagrden has walked more frequently than Still this year. He could finish his season particularly strong now that he’s playing half his games in a windy, fly-ball-friendly home stadium.

Jed Lowrie

Boston Red Sox | SS | 23 years old
Lowrie might be the most underhyped prospect playing for a big-market baseball franchise. He struggled with an ankle injury in 2006 and fell under the radar of most fans as fellow 2005 draftees Jacoby Ellsbury and Clay Buchholz emerged as top prospects. In 2007, Lowrie has remained healthy while holding his own at shortstop and demonstrating solid on-base skills and above-average power for a middle infielder.