Looking back at Koji Uehara’s time with the Red Sox

If you’ve been watching baseball the last few years, few things are more obvious than the increase in velocity around the game, primarily among relievers. It seems that every relief pitcher comes in from the bullpen and throws 95 mph or harder. While on average that isn’t specifically true, the rise in reliever velocity is undeniable.

Since 2007, average velocity among relievers has gone from 91.4 to 93 mph. While that may not sound like a huge jump to the average fan, it is a big difference. Even a 1 mph increase in velocity can upset a batter's timing.

That being said, while reliever velocity has made a steady climb over the years, some pitchers have been able to survive without throwing gas. Koji Uehara, who throws around 88 mph, has peripherals that are comparable to those of Dellin Betances. Uehara can strike out batters with the best of them, and he does it without a high-octane fastball.

Pitchers who throw that softly typically don’t strike out oodles of batters. But, Uehara is one of those rare pitchers who was able to pull that off. What made him even more unique, however, was his ability to do this without issuing many walks. From 2013 to 2016, Uehara managed to only walk 1.47 hitters per nine innings, which ranked fifth in all of baseball during that time.

Koji would sometimes go on remarkably long streaks without allowing a walk. There was one instance in particular when Uehara didn’t allow a walk for 44 and 1/3 innings over 36 games, which is close to a full season’s worth of work for some relievers.

With his control and strikeout prowess, Uehara had one of the best strikeout to walk ratios in all of baseball during his time with the Red Sox.

The average strikeout to walk ratio during that time span was 5.5. Uehara’s was 84% better than that, and he did it without a 90 mph fastball.

That doesn’t mean that Koji has a bad fastball. In fact, it was a source of constant amazement that a pitcher who didn’t even hit 90 on a regular basis could get so many swings and misses with the pitch. Since the PITCHf/x era began Uehara ranks 20th (min 1000 pitches, data from Baseball Prospectus) in fastball swing and miss rate. He’s the only reliever in the top 50 in that category who sits below 90 MPH.

Many people have tried to explain this phenomenon, and the reality is that there isn’t one great answer. Rather, Uehara did multiple things well as a pitcher. First, he had one of the best splitters among any relief pitcher during that time frame. In fact, his splitter ranks 4th in the PITCHf/x era with a 42% whiff rate.

Uehara has always been able to utilize these two pitches in tandem to keep hitters off balance.

His fastball is straight with very little movement, while his splitter has the third most horizontal and vertical movement in the PITCHf/x era, making it one of the most difficult pitches to hit in all of baseball.

The hardest part for hitters, though, is figuring out which one was coming next. Uehara usually threw both pitches at around the same rate, especially in Boston, with a little bit of a cutter mixed in every now and then.

Overall, from 2013 to 2016, Uehara ranked 10th in all of baseball in reliever PWARP (Baseball Prospectus’ pitcher WAR variant, which utilizes the great DRA metric as a component) with 5.99. He would have ranked higher had it not been for a bit of a home run bugaboo. While Uehara was certainly a great relief pitcher, he still was more susceptible to the long ball than the other pitchers ranked around him. This was probably due to his velocity.

Simply put, the slower you throw, the smaller your margin of error is on any given pitch. If your pitch is down the middle or even slightly off its mark, there’s a better chance the hitter will connect and there’s a better chance that he will punish you for that mistake. The harder a pitcher throws, the less time a hitter has to react, therefore, the less time that hitter has to react to your mistake. .

Now, even though Uehara wasn’t the best reliever in baseball during that time, he’s one of the better relief pitchers in the game. At 41, he’s obviously past his prime, and last year, Uehara struggled more than normal.

That said, he still had an incredible run with the Red Sox. He eventually lost his job to Craig Kimbrel, who is younger and deadlier. Yet Ueheara was still a driving force for the 2013 Red Sox, and was one of the hallmarks of their World Series run. He will not soon be forgotten in Boston.

Julien Assouline is a contributor at Beyond the Box Score. He’s written for Baseball Prospectus, The Hardball Times, and BP Milwaukee. You can follow him on twitter @JulienAssouline