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Billy Butler and the best young hitters in baseball

Zack Greinke has obviously been the big story for the Royals this year, but Sam Mellinger of the Kansas City Star notes that Billy Butler is at least giving fans a second reason for optimism while the team tries to avoid losing 90-plus games for the eighth time in a dozen seasons:

Billy Butler, barely 23 years old, is showing some real signs of turning into the first legitimate middle-of-the-order hitter the Royals have developed since, what, Sweeney? Four hits yesterday, including two doubles, raised his line to .293/.344/.449. ... Since June 10--we're talking 18 starts and 81 plate appearances, roughly one-eighth of a season--Billy is hitting .333/.370/.520, with five doubles, three homers and nine RBIs.

Butler was one of my "breakout" picks this season, so I'm happy to see him thriving after the Royals demoted him to the minors following a slow start last year. He hit .336/.416/.561 in the minors despite being extremely young for every level, never posting a batting average below .290 at any stop, so it was only a matter of time before Butler started knocking around big-league pitchers too.

Mellinger's blurb about Butler got me curious about how well his production compares to other 23-year-olds and in the bigger picture how well various other young hitters are faring this season. With that in mind--and with the help of utterly indispensable Baseball-Reference.com--here's a look at how the youngest hitters in baseball are doing in 2009, broken down by age group:

20-YEAR-OLDS         PA      AVG      OBP      SLG     OPS+
Elvis Andrus        232     .269     .330     .380      87

I've set the cutoff for this little study at 200 plate appearances, but Elvis Andrus is actually the only 20-year-old hitter in all of baseball with even 100 trips to the plate this season. In fact, Fernando Martinez of the Mets is the only other 20-year-old to bat at all this year unless you count Tigers starter Rick Porcello's work at the plate during interleague play.

While not especially productive Andrus has certainly held his own at the plate, which is an extremely promising sign from a 20-year-old shortstop who didn't do a whole lot of hitting in the minors. Andrus has been fantastic defensively, rating 5.3 runs above average in 65 games according to Ultimate Zone Rating, so even slight improvements offensively would make him an All-Star-caliber player.

21-YEAR-OLDS         PA      AVG      OBP      SLG     OPS+
Justin Upton        315     .309     .387     .558     141

I've been fawning over Justin Upton in this space all season, so it shouldn't surprise you to learn that he's a) the only 21-year-old with more than 200 plate appearances and b) knocking the cover off the ball. Upton currently has the 18th-best adjusted OPS+ of all time for a 21-year-old, with Mickey Mantle and Hank Aaron tied for the spot above him. He's on pace to hit .309 with 30 homers, 40 doubles, 75 walks, and 20 steals, and has also been outstanding defensively in right field. Stud.

22-YEAR-OLDS         PA      AVG      OBP      SLG     OPS+
Pablo Sandoval      298     .327     .379     .548     142
Colby Rasmus        256     .271     .313     .453     102
Jay Bruce           308     .215     .295     .458      94

Pablo Sandoval has quickly become one of my favorite players, because the man they call "Fat Ichiro" or "Kung Fu Panda" has hit .327 with a .548 slugging percentage despite swinging at everything and running the bases like he's jonesing for a piece of cake. Combined with his 41-game debut last season Sandoval has hit .333/.372/.528 through 452 plate appearances in the majors.

23-YEAR-OLDS         PA      AVG      OBP      SLG     OPS+
Evan Longoria       316     .297     .377     .558     139
Adam Jones          310     .300     .355     .502     120
Billy Butler        303     .289     .340     .443     107
Asdrubal Cabrera    243     .307     .364     .417     103
Dexter Fowler       293     .250     .340     .381      87
Chris Davis         270     .203     .259     .422      76

This is Butler's age group and as you can see he fares pretty well, ranking third in adjusted OPS+ behind only Evan Longoria and Adam Jones, although he's also been less valuable than Asdrubal Cabrera once defense is factored in. Longoria has been one of the most valuable players in the league through three months, while Jones currently has the 27th-best adjusted OPS+ ever for a 23-year-old center fielder.

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