To no one’s surprise, a Red Sox pitcher who came over from Japan last offseason is now an American League All-Star. It’s which Japanese Red Sox pitcher that’s the shocker-Hideki Okajima made the All-Star team last Thursday, the winner of the fan vote that selects the last representative in each league. It’s not a bad pick. Okajima is having an amazing season, with an ERA of 0.83, 37 strikeouts, 12 walks, and just one home run allowed-and that was to the first batter he faced this year. He certainly benefited from the online voting, which enabled his global fan base to be heard.

You can’t say enough about his impact on the Red Sox, either. In mid-March, the team’s bullpen was in flux, with Jonathan Papelbon headed for the rotation and no clear closer candidate. Papelbon gets most of the attention for what he’s done in the ninth inning, but Okajima’s effectiveness in the eighth has made the Sox very difficult to beat late in games. He’s not just a specialist either, although his ability to get left-handed hitters out proved to be very valuable in the Red Sox’ early-season matchups against the Yankees.

Is he the Sox’ best Japanese pitcher, though? After all, despite seeing his ERA rise above 5.00 early this season, thanks in no small part to a rough schedule, as predicted Daisuke Matsuzaka has become one of the top 10 starters in the American League. With his work complete through the All-Star break, Matsuzaka ranks 13th in SNLVAR, 14th in VORP for pitchers, third in strikeouts, and fourth in strikeout rate. Yesterday’s poor start against the Tigers served to knock him out of the top 10 in many categories; it was the first time since May 30 that Matsuzaka had failed to post a quality start.

Which of the two performances is better? Comparing relievers and starters can be complicated. We can start with one of my favorite tools, looking at the difference between the output of the two pitchers:

Pitcher        IP    H   R   ER   BB   SO   HR   ERA
Matsuzaka   119.2  110  51   51   38  123   12  3.84
Okajima      43.1   24   4    4   12   37    1  0.83
Difference   76.1   86  47   47   26   86   11  5.54

The American League’s ERA is 4.44, and its RA is 4.89. The performance difference between the two lines is below average but well above replacement level, so you can argue that Matsuzaka’s value is higher than Okajima’s, as the Sox are better off with his extra innings as opposed to what a replacement-level pitcher would provide. You can get to this conclusion as well by looking at the runs each pitcher has saved. Despite his big edge in ERA, Okajima has saved 24 runs as compared to a replacement-level pitcher, but Matsuzaka has saved 51.

An eighth-inning reliever should gain some value by weighting his performance by the high-leverage situations in which he pitches, but Okajima’s Leverage score of 1.28 isn’t particularly high. He ranks behind not only most closers, but a slew of his peers in the set-up realm. There’s not enough bounce from leverage to elevate the value of Okajima’s performance beyond that of Matsuzaka’s.

That Matsuzaka had a bad start after the teams were selected makes all of this look a lot closer than it is. At the time the final ballot was assembled, Matsuzaka was having a stronger season that his teammate, and would have been a better candidate for the All-Star team. Without taking anything away from Okajima, it’s clear that Matsuzaka has been the better Japanese hurler for the Red Sox.

Some general admininstrative notes:

  • I was going to write about the Yankees/Angels game, and my first trip to the Stadium in six years, but it was 10-0 in the bottom of the fourth, leaving me without much material. I’ll get an Unfiltered up about it today.
  • It’s Free Week here at Baseball Prospectus, so if you have friends who don’t subscribe, get the word out that they can read all our great content-and Prospectus Today, too-for free, and find out what BP is all about.
  • Nate Silver is in San Francisco for the All-Star Game. He’ll be doing a live chat tomorrow night as the game begins.

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