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FiveThirtyEight

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The New York Yankees faced a tight spot on July 9 at Progressive Field in Cleveland. Their newly acquired starting pitcher, Brandon McCarthy, had gutted his way through 6.2 innings, lacking his best stuff but still holding the Indians to four runs, just one of those earned. Locked in a 4-4 tie, manager Joe Girardi turned to his bullpen, knowing it had no margin for error.

The first pitcher out of the pen was Matt Thornton. Instead of battling Indians hitters with an assortment of southpaw soft stuff, Thornton fired two straight fastballs to All-Star outfielder Michael Brantley, the second one resulting in a harmless, inning-ending groundout. The radar gun flashed a reading on Thornton’s heater: 97 mph.

The next Yankees pitcher to toe the rubber was Dellin Betances. A 26-year-old rookie, Betances had taken the long route to establish himself in the big leagues. At 6’8” and 260 pounds, he was once a promising starter prospect, but struggled mightily to make use of his huge frame. Converted to relief last season, Betances simplified his repertoire, leaning on his blazing fastball and nasty slurve. The result was a breakout season in a repeat stint at Triple-A, followed by a job in this year’s Yankees bullpen. On this night against the Indians, Betances needed only 10 pitches to retire the side in the eighth inning. The four fastballs he threw in that frame averaged a tick below 99 mph.

As the night wore on, a battalion of flamethrowers kept emerging out of the Yankees bullpen. Adam Warren tossed 1.1 scoreless innings, firing 12 fastballs that averaged 95 mph. After David Huff (94 mph) struggled with three batters, Shawn Kelley (94 mph) bailed him out with 1.2 scoreless. The Yankees finally scored a run in the top of the 14th, prompting David Robertson to take the mound. New York’s closer needed 14 pitches to set down the Indians in the bottom of the inning, clinching a 5-4 win for the Yanks. Unlike many of his relief-mates, Robertson almost never throws a four-seam fastball, the kind of straight heat that tends to register the highest radar gun readings. Instead, he throws the cutter, a pitch that bores in on left-handed batters, inducing countless weak groundouts and often chopping their bats into tiny splinters. That night against the Indians, Robertson’s cutter velocity peaked at 95 mph, averaging “only” 93 — a necessary trade-off to get the kind of movement that can cause sleepless nights for its helpless victims.

The Yankees are hardly alone in their employment of multiple cheese-huckers. Teams are trotting out pitchers who routinely throw mid-90s fastballs, with gusts up to the high 90s, and occasionally 100 mph or better. Most of those fireballers work out of the bullpen, and they’re needed more now than ever before. In a chicken-and-egg scenario, starters’ inability to go deep into games has created heightened demand for fresh and electric arms out of the bullpen.

Thanks to Baseball-Reference.com, we can track the upward trend in reliever use over the past 50 years:

keri-feature-relievers-1

The broader trend that goes back half a century is clear. In 1964 (four years after the save rule first came to baseball), teams used an average of 2.58 pitchers per game, including the starter; today, they’re using 3.92 pitchers per game. In ’64, relievers tossed an average of 2.64 innings per game; today, they’re throwing an eyelash more than three innings per game. Starters are getting yanked much earlier now than they did during Willie Mays’s heyday, and relievers are shouldering a greater percentage of the pitching load. But what’s most striking is how much bigger the jump is in the number of pitchers used per game as compared to number of relief innings thrown per game.

Bullpens weren’t always like this. In 1960, sportswriter Jerome Holtzman introduced the save statistic to baseball. Holtzman wanted a way to better recognize the impressive contributions of pitchers like Joe Page and Hoyt Wilhelm, relief aces who came out of the bullpen to replace tiring starters, often throwing multiple innings at a time. Over the ensuing 25 to 30 years, bullpens slowly evolved, to the point where managers started to ease back on the role of multi-inning stoppers.

The person often credited with the next wave of changes is Tony La Russa. The former White Sox, A’s and Cardinals manager figured he could squeeze more value out of his bullpen by placing a greater emphasis on putting specific relievers in a spot where they’d have the best chance to succeed. If you want to know why a contemporary manager may use three different relievers in a single inning in the name of getting the lefty-on-lefty and righty-on-righty matchups he wants, you can give a lot of the credit (or blame, if you’re not a huge fan of three and a half-hour games) to La Russa.

Still, today’s managers might not be so willing to change pitchers so frequently1 if they didn’t have all those guys waiting in the bullpen who can throw 95-100 mph at will. So, using FanGraphs fastball velocity data, we set out to answer the question: What percentage of relief pitchers throw 95 mph or better today, as compared to past seasons?

keri-feature-relievers-2

Though reliable velocity data only goes back to 2002, that’s still a big spike in a relatively short amount of time: We’re only two-thirds of the way through this season, and already we’ve seen nearly twice as many innings thrown by relievers who average 95 mph or higher on their fastballs than we did just 12 years ago.

OK, so we know that managers are using more relievers, and that more of them throw hard. But what matters is whether bullpens are performing better.

To measure this phenomenon, we ran another Baseball-Reference query and found that the average bullpen’s OPS+ allowed2 has dropped dramatically over the past 45 years, from 103 (3 percent worse than the overall league average, a number that includes starters and relievers) in 1969 to 94 (6 percent better than average) this season. The performance disparity between relief pitchers and starters really began to accelerate in the mid- to late 1990s, as the post-La Russa bullpen era fully took hold.

keri-feature-relievers-4

Note how the shaded area of the chart is wider than it used to be. As recently as 1988, the OPS+ allowed by starters and relievers was almost equal; now, relief pitchers are consistently hurling much sharper innings than starters. It’s a change that also goes hand in hand with the aforementioned increase in relievers deployed per game. Managers have gotten wise to the fact that more innings should go to the more effective subgroup of pitchers, and that they’re even more effective when called upon in waves to throw aspirin pills past helpless batters.

This data gives us a good idea of the “what.” Figuring out why relievers are getting so much faster and so much better is trickier, because it’s more subjective. It’s possible that teams are doing a better job of recognizing which pitchers should be converted into relievers and which ones should remain starters. In the same way the Yankees figured out that Betances was much better suited to relief work, the Cincinnati Reds resisted the temptation to make Aroldis Chapman a starter and let him unleash his electrifying fastball in the closer role instead. Chapman alone might be skewing our data set somewhat, given the frequency with which he launches blinding fastballs, and the incredible results he produces. According to the excellent site Baseball Savant, Chapman has thrown a staggering 257 fastballs that have topped 100 mph this year; every other pitcher in the majors has combined to throw 103 of them.

Earlier this year, in an an article about the recent increase in Tommy John surgeries, I discussed why we might be seeing more pitchers assaulting radar guns than ever before. One frequently cited theory holds that kids are specializing in one sport at an earlier age, so once they lock in on baseball they’re building arm strength and pitch velocity more quickly, but also making themselves more susceptible to future injury. That so many can throw so fast, and so many hit the disabled list, makes relievers fungible (with a few exceptions like Betances and Chapman). As a result, managers choose a few relievers from a phalanx of fireballers, then go get a few more if some of them break down.

In other words, the pitchers might be on the mound for fewer and fewer pitches, but the trend of harder throwers looks like it’s here to stay.

Footnotes

  1. La Russa gained the greatest notoriety for his pitching changes while in Oakland, when he helped turn situational lefties like Rick Honeycutt into valuable late-inning weapons. But we can’t put all of this on La Russa: Managers use slightly more than one extra pitcher per game, on average, since 1989, La Russa’s one World Series-winning season with the A’s. ^
  2. That is, on-base plus slugging percentage allowed, re-scaled so that the MLB average is always 100. ^

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