As bullpen ERAs fall, clubs rise up standings

The Cardinals, Royals, Dodgers, Astros, Yankees and Mets are the top six teams in the Majors in relief ERA.

Oh, and they also happened to be leading their respective division.

Can't be a total coincidence, can it?

Sortable team statistics

Naturally, a season this long produces a multitude of statistical swings and sways. The Tigers, for example, have one of the highest bullpen ERAs in the Major Leagues (4.07), and they've commanded the top spot in the American League Central often this season.

But there is an overarching sense in today's game that the correlation between relief success and team success is stronger than at any other point.

Up-to-the-minute standings

"I'm not sure exactly when things changed," Cardinals general manager John Mozeliak said, "but I do think with how postseasons games are played, teams with stronger bullpens tend to win. The game comes shorter, and in our environment of less run expectancy, this puts enormous pressure to score early."

Mozeliak's right. Last season, we saw a 2.7 percent rise from the year before -- from 73.8 to 76.5 -- in the number of instances in which a team leading after three innings went on to win a game.

The pressure on offenses early in games is heightened by the way managers have increasingly worked mid-inning matchups in their favor by utilizing deep bullpens. Relievers this season are accounting for 35.2 percent of total batters faced, a rise from 33.1 percent five years ago.

Beyond the workload, though, is the way it is distributed.

Between 2005 and '14, there was a 21 percent jump in the number of instances in which a reliever faced just one batter, and batters are struggling with this kind of specialization. Just look at the differences between how batters have fared against relievers and how they've fared against starters this decade.

As you can see, last season was the first this decade in which the difference in on-base plus slugging percentage against starters and against relievers didn't increase from the year before, though the early sample this season seems to indicate we're back on track in that particular department.

Clearly, then, the idea of knocking out the opposing starter in order to "get to the bullpen" is outdated, which is why some of MLB's offensive stars have taken a more aggressive approach at the plate this year.

Bullpens are more dynamic than at any time in recent memory. To wit: The average fastball velocity out of the 'pen this season, per FanGraphs, is 92.3 mph, more than a full mph higher than a decade ago (91.0). But hitters have way more than just velo to worry about. The percentage of pitches thrown by relievers that can purely be identified as "fastballs" has declined 5.1 percent in the past decade, with pitches that break -- namely, the slider (up 1.5 percent) and cutter (up 4.7 percent) -- gaining more prominence.

"The guys that come out of our bullpen are multiple-pitch guys; they're not just one-dimensional," Royals GM Dayton Moore said this spring. "You've got to be able to execute pitches, and hopefully, you have multiple pitches in your arsenal that you can execute. Those three-pitch guys are pretty much regulated as starters, but we try to make sure our bullpen guys can develop multiple pitches and be efficient."

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It says something about today's game that a once-perennial powerhouse like the Yankees spent their offseason trying to emulate the small-market Royals -- a team that rode its relievers to the World Series last season -- by prioritizing the 'pen. More than one-third of the Yanks' total offseason expenditures went to a single reliever (Andrew Miller) with one career save to his name prior to 2015, because the Yankees knew Miller could join Dellin Betances to form a monster late-innings pair.

As far as in-season usage is concerned, Mozeliak's Cardinals might turn out to be an interesting case study. Tony La Russa was notorious for his matchup usage with his bullpens, but the Cards have doled out a higher percentage of the workload to their relievers even since La Russa's final season in 2011.

The 'pen, then, has played an integral part in the Cardinals' hot start this season, accounting for a greater percentage of the workload than it did just one season ago. This is an especially pertinent point with staff ace Adam Wainwright out the rest of the season with a torn left Achilles tendon.

"The key," Mozeliak said, "is to have relievers that give you flexibility and are not restricted to specific roles."

Teams are wise to prioritize that flexibility, because bullpens appear to be playing an increasingly pivotal role in the overall outcome.

We've got the standings to prove it.