Friday night's scolding of the Colorado Rockies marked the end of Clayton Kershaw's 2013 regular season. The southpaw has now completed six sensational years at the major league level, and over the past half-century, few other pitchers have realized comparable success at such a young age.
Not yet 26 years old, the All-Star left-hander has led the National League in earned run average for three consecutive summers. According to FanGraphs, he also boasts the lowest earned run average in the majors since debuting in 2008 (min. 400 IP). His 1.83 ERA this year is the best posted by any qualified starter since Pedro Martinez in 2000.
We'll look at how Kershaw's first half-dozen MLB campaigns stack up against those of all others who have debuted since 1964. More specifically, we're intrigued by those who reached the The Show early—Kershaw was called up to the Los Angeles Dodgers as a 20-year-old—and quickly proved themselves to be both dominant and durable.
Identifying Legitimate Challengers
Let's begin with a list that includes all pitchers of the past 50 years who amassed at least 1,000 innings through their age-25 campaigns. Check it out on either the Baseball-Reference.com Play Index or FanGraphs (whichever color scheme is easier on your eyes).
There are only 44 names, including a handful of Hall of Famers and a few strong candidates for future induction, as well as plenty of former stars who couldn't make the necessary adjustments as they matured.
Using either source of Wins Above Replacement, Kershaw cracks the top 10. He's just as impressive in terms of adjusted earned run average, batting average against, OPS against, quality start percentage and strikeout-to-walk ratio.
Indeed, it's at least worth discussing whether or not the start of his career is the best of these past several generations.
The following pitchers contended with Kershaw for the top spot in all of the aforementioned categories, and therefore received serious consideration: Bert Blyleven, Roger Clemens, Doc Gooden, Bret Saberhagen, Tom Seaver and Fernando Valenzuela.
(Sam McDowell was on par with those guys from 1964 to 1968, but actually debuted back in 1961. He struggled during his first couple of seasons and never really solved his command issues.)
Kershaw Isn't No. 1
Sorry for spoiling the suspense, but Kershaw frankly doesn't belong in the same sentence as the young versions of Blyleven or Seaver.
Here's a comparison of their rookie campaigns. Keep in mind that for IP, ERA+ and K/BB, higher is better:
Blyleven was actually the youngest player in the entire American League during his debut season. Thanks to that early call-up, he has posted by far the highest 25-and-under career WAR of any pitcher over the past 50 years.
Breaking through in the 1970s deprived Blyleven of the major award recognition that he sorely deserved. Sportswriters overlooked him because of a pedestrian win-loss record. He was 108-101 overall through age 25 and never better than five games above .500 in a season. Nonetheless, he had a virtually identical quality start percentage to Kershaw at those ages, not to mention 115 complete games and 30 shutouts.
Meanwhile, Seaver kicked off his career with several more years of life experience, and his immediate excellence reflected that. He earned National League Rookie of the Year honors in 1967 and the NL Cy Young Award in 1969. Tom Terrific logged at least 250 innings in each of his first six seasons, whereas Kershaw has never reached that milestone.
The adjusted earned run average and batting average against of 2008 to 2013 Kershaw and 1967 to 1972 Seaver practically match, but remember that Seaver was frequently pushed into the later innings or used on three days' rest (often both).
Valenzuela Peaked Early, Saberhagen Wasn't Steady
On the other hand, Kershaw belongs ahead of both Fernandomania and Sabes considering their inconsistencies.
Valenzuela was unstoppable for much of the strike-shortened 1981 season. He led the National League in innings pitched and strikeouts at age 20 en route to the NL Cy Young Award.
Unfortunately, the Mexican lefty couldn't sustain that excellence. Although nearly as effective in 1982, his WHIP bloated to 1.34 the following season. Then in 1984 and 1985, walks became somewhat of a concern (3.66 BB/9 and 3.34 BB/9, respectively).
Of course, Valenzuela was still a great pitcher in his mid-20s, just not on par with what Kershaw has been for the Dodgers the past several years.
This coming offseason, Kershaw will join Saberhagen in an elite fraternity of pitchers to hoist two Cy Young Awards prior to turning 26. The difference is that Kershaw was more productive in his non-award-winning campaigns.
L.A.'s present-day ace didn't take home the hardware in 2009, 2010 or 2012, but he still posted adjusted earned run averages of 143, 133 and 150, respectively. Saberhagen pales in comparison, as he only totaled 156 innings and a 102 ERA+ in 1986 (following his first award). After an outstanding '87 season, he regressed again in 1988. In that era, it wasn't acceptable for a rotation leader to go a full year without recording a complete-game shutout, yet that's exactly what happened.
Deciding No. 3, No. 4 and No. 5
Kershaw, Gooden and Clemens. Kershaw, Clemens and Gooden. Gooden, Clemens and Kershaw. Gooden, Kershaw and Clemens. Clemens, Kershaw and Gooden. Clemens, Gooden and Kershaw.
Those are our six options.
Among these pitchers, who had the best start to an MLB career?
Actually, we can narrow them down to three. Clemens had the obvious early career edge over Kershaw.
Their MLB debuts were eerily similar—Clemens had a 97 ERA+ and 8.5 K/9 in 1984, much like Kershaw's 98 ERA+ and 8.4 K/9 in 2008.
They diverged, however, after Clemens' rotator cuff surgery in '85. With a little help from Dr. James Andrews, the Rocket came back better than ever. Comparing their third, fourth and fifth years, he beat Kershaw in ERA+ (154 to 148) and K/BB (3.70 to 3.48) while averaging about an extra inning per start.
So...Kershaw, Gooden and Clemens. Kershaw, Clemens and Gooden, Gooden, Clemens and Kershaw. Gooden, Kershaw and Clemens, Clemens, Kershaw and Gooden. Clemens, Gooden and Kershaw.
Gooden was initially far superior to Clemens and Kershaw. He made 66 regular-season starts through age 20, unbelievably maintaining a 176 ERA+, 1.01 WHIP and 9.9 K/9. Then again, being less than stellar from ages 21 to 25 negates that (110 ERA+, 1.20 WHIP, 7.4 K/9). He ranks last among this trio as a result.
In other words, relative to other pitchers from the past five decades who were moved into MLB starting duty so early in life, Kershaw has bolted to the fourth-best start. He's only looking up at two Hall of Famers and a third icon who's a G.O.A.T. candidate (albeit with an asterisk).
Kershaw's agents, Casey Close and J.D. Smart, would be wise to quote that paragraph when they negotiate a long-term contract with the Dodgers this winter.