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Koji Uehara's Strikeout to Walk Ratio

You probably know that Koji Uehara is really good. Let's look at just how good he's been on a historic level.

Stephen Brashear

For his career as a reliever, Koji Uehara has a 10.31 strikeout to walk ratio.

Literally speaking, that's the article! If you'd like to keep reading though, we can put some context behind that number.

Ten is sometimes a big number, especially on hypothetical scales of one to ten, but most things aren't on scales, of any sort. Regardless, in this case, ten is a big number. That 10.31 mark ranks first all-time among qualified relievers. Let's start on how we get to that figure:

K/9 BB/9 K% BB%
Uehara 11.63 1.13 34.7% 3.4%

That chart consists of big numbers, small numbers, and nothing in between. The second highest K:BB ratio belongs to Uehara's teammate and fellow countryman Junichi Tazawa, at 6.88. Tazawa, however, just makes the 'qualified' mark of 100 innings pitched, with 113. Uehara isn't exactly Trevor Hoffman, but his sample is decent: 207 innings.

Third on the list is Dennis Eckersley, at 6.29.  "Which shape is unlike the others?" says the kindergarten teacher.

Reliever K:BB ratio
1 Koji Uehara 10.31
2 Junichi Tazawa 6.88
3 Dennis Eckersley 6.29
4 Sergio Romo 5.86
5 John Smoltz 5.60
6 Edward Mujica 5.25
7 Jonathan Papelbon 4.81
8 Craig Kimbrel 4.63
9 Sean Doolittle 4.54
10 Rafael Betancourt 4.50
11 Sammy Ellis 4.46
12 Kenley Jansen 4.42
13 Eric Gagne 4.35
14 Mariano Rivera 4.24
15 Dick Hall 4.19

Of course, strikeout to walk ratio is just one way to measure performance. Mariano Rivera is widely considered the greatest reliever of all-time, and not just for his longevity. His ratio is less than half of Uehara's.

While Uehara isn't on Rivera's level overall, having an excellent ratio sure doesn't hurt. Uehara trails just Craig Kimbrel in career ERA at 2.00, and right in front of Mo at 2.06. His 0.72 WHIP is number one all-time.

On the more advanced metrics, Uehara isn't quite as impressive mostly due to his shaky home run rate. Still though, his 2.42 FIP is seventh among qualifiers.

David Schoenfield at ESPN uses Uehara as just another example to dispel the closer mentality myth. The Red Sox let Jonathan Papelbon walk, Joel Hanrahan has missed the entire season, Andrew Bailey has been hurt, and they haven't missed a beat in the ninth inning. Schoenfield's article simultaneously praises Uehara while also stating that closers and other effective relievers are replacable-- a backhanded compliment of sorts.

Relievers are indeed easier to replace than most other positions, but what Uehara has been doing is on another level. He won't end his career as one of the greatest relievers of all-time, due to his late arrival in the States.  But as you can hopefully see above, his rate stats are simply off the charts, and he's been doing it for years.


So how do you register ten times any many strikeouts as walks? After all, we use this ratio because they are often at odds. If you don't walk many batters, you usually have to throw it in the zone frequently. If you want to reduce contact and strike out more batters, though, it often requires throwing out of the zone.

The elixir to all this is getting hitters to chase when you do go out of the zone, and turns out Uehara is the best at doing just that. We're striking a deceased equine here, but his 41.0% O-Swing percentage again ranks first all-time among relievers. The contact rate he induces on those swings is actually rather pedestrian, at 62.3%. But when you get hitters to swing at balls that frequently, it's not a huge surprise that Uehara's Swinging Strike percentage is fourth all-time. Using that figure, he is in some pretty elite company:

Reliever SwStr %
1 Eric Gagne 18.5%
2 John Smoltz 17.3%
3 Brad Lidge 17.0%
4 Koji Uehara 16.3%
5 Craig Kimbrel 15.8%

Not a single player among the top thirty in Swinging Strike percentage also has an O-Swing percentage above 38%. What was interesting to me is that Uehara generates whiffs in the zone as well. His 74.7% Z-Contact mark is right in line with the other pitchers on the list. He also doesn't throw in the zone at a particularly high level.

This is somewhat surprising, of course, because Uehara's stuff is not overwhelming. His fastball velocity would be below average for a starter, let alone a closer, at 88.3 mph for his career. He throws his four-seamer 57% of the time (less often in recent years), with the remaining being his splitter and a sprinkling of cutters. It's not a power split either, a la Roger Clemens- at just 80.6 mph, it essentially acts like a changeup.

The narrative I would have guessed before looking under the hood would be that Uehara pounds the strike zone, but when he does go out of the zone, he's impossible to hit due to his splitter's vertical movement. Turns out he's hard to hit whether it's in or out of the zone, and on a percentage basis, he's actually doesn't miss that many bats out of the zone.

But he gets hitters to chase so frequently, and that's how he never walks anyone. It's a bit of chicken and egg here--this is likely tied to the fact that he does have such great command and control-- so hitters are looking to put the ball in play instead of waiting for the pipe dream base on balls.

Perhaps it's also because he seems hittable and that batters are looking to do damage--and sometimes they do, given his home run tendencies. In the big picture though, it's more than a tolerable trade-off.

As to why a straight 88 mph fastball and 80 mph splitter registers swing and misses like Kimbrel and Lidge's heat and slider combo- I'd have to leave that to a major league hitter's account. I'm still surprised at how low his Z-Contact percentage is.

But back to the walk rate, maybe having less-than-explosive stuff is related not only to the pitches being more controllable, but also the hitter's aggressiveness. His overall Swing percentage of 55% is high relative to the other guys on those lists, and Uehara takes full advantage of those hacks. He doesn't always throw in the zone, but he rarely throws balls.

That's how you have a 10:1 strikeout to walk ratio, and that's how Uehara is different from some of those other amazing relievers. Uehara is probably most well-known for being in the Chris Davis trade, but his performance on a rate basis ranks up with some of the best relievers of all-time.

. . .

Statistics and swing percentages courtesy of FanGraphs.

Andrew is a contributor at Beyond the Box Score. You can follow him @AndrewShen_SF.