As my friend David Schoenfield pointed out earlier today, according to Baseball-Reference.com the 10 pitchers most similar to Clayton Kershaw through age 23 were, in order of similarity, Vida Blue, Dontrelle Willis, Hal Schumacher, Ramon Martinez, Jimmy Dygert, Dean Chance, Dave Boswell, Ismael Valdéz, Al Mamaux, and Ken Holtzman.
That's a little misleading, though, because similarity scores are based on raw statistics, taking into account little or no context. Here are those same pitchers, but this time in order of ERA+ (ERA relative to league, with adjustments for home ballparks):
135 Clayton Kershaw
133 Dean Chance*
128 Ismael Valdéz
125 Dontrelle Willis
122 Vida Blue
120 Al Mamaux
119 Hal Schumacher
114 Ramon Martinez
106 Ken Holtzman
104 Dave Boswell
097 Jimmy Dygert
With the exception of Dygert, who pitched in the Dead Ball Era, all of these guys did pitch well. If they hadn't, they wouldn't have made the list. But many of them did their pitching in eras more pitcher-friendly than Kershaw's. When we adjust for eras (and ballparks), Kershaw obviously jumps to the head of the class.
But those next three pitchers on the list do make for the beginnings of a sad cautionary tale.
At 23, Dean Chance won the American League Cy Young Award; also, just like Kershaw, he won the pitcher's Triple Crown, leading his league in wins, ERA and strikeouts. He would enjoy four more solid seasons, after which his career went into the toilet real fast.
Ismael Valdéz, different story but also sad. He lasted for eight seasons after his outstanding Age 23 campaign, but was never really the same. After racking up that pretty 128 ERA+ through 23, he was just 94 for the rest of his injury-plagued career and managed double-figure victories (11 and 14) in two of those eight seasons.
And Dontrelle Willis, you know about. In the six seasons since his Age 23 season -- after which he finished second in the Cy Young balloting -- Willis has gone 26-42 with a 5.02 ERA.
What does all this tell us about Clayton Kershaw, specifically?
Not much. Except that the past does not perfectly predict the future, especially when it comes to young pitchers. There is an excellent chance that Clayton Kershaw will never again pitch as well as he did when he was 23 years old. The Dodgers were smart to get Kershaw's signature on a two-year, $19 million contract. But history does suggest that Kershaw will not still be a great pitcher four or five years from now.
I told you it was a sad tale.