Commentary

The Components of ERA

Updated: February 15, 2012, 2:40 PM ET
By Tristan H. Cockcroft | ESPN.com

Editor's note: This story was originally published in the 2011 ESPN Fantasy Baseball Draft Kit. It is being republished unaltered here for your convenience.

ERA, or earned run average, is one of the most instantly recognizable, frequently cited measures of a pitcher's performance.

The problem: It's also one of the most misleading measures for forecasting future success … and forecasting future success is the name of our game.

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Sure, ERA accounts for two of the most critical skills of a pitcher -- recording outs and preventing runs -- but many external factors impact those departments, often skewing the results. Even the Wikipedia page for earned run average hints at its misleading nature, noting that "because of the dependence of ERA on factors over which a pitcher has little control, forecasting future ERAs on the basis of the past ERAs of a given pitcher is not very reliable and can be improved if analysts rely on other performance indicators such as strike out rates and walk rates."

That's not to say ERA is entirely without value. For one thing, it remains one of the five primary Rotisserie categories. But before you blindly assume that a pitcher's low past-season ERA -- or even his three-year ERA -- portends future success in the category, be sure to consider its context. This is something we do every season when formulating our projections, and it helps explain how a pitcher like Clay Buchholz, who had the majors' third-best ERA in 2010 (2.33), can be projected to have an ERA more than run higher (3.35) in 2011.

Instead of taking Buchholz's 2.33 -- or similarly successful or unfortunate pitchers' ERAs -- at face value, instead, consider that any or all of the following factors might have had a strong influence on the final numbers.

Unearned runs

In a literal sense, of course unearned runs have no impact on ERA; earned runs are the ones included in the calculation. But unearned runs are the product of faulty defense, a result of an error or passed ball, and while a pitcher doesn't get charged for many of the runs he allows after such a mistake, for evaluation purposes maybe he should. (At the same time, maybe he should get credit for the outs he would have gotten when an error instead occurred.) Remember, recording outs is the most critical task for a pitcher, and just because his defense lets him down, his skills should be strong enough that he's capable of converting four -- sometimes more -- outs in a single inning when necessary. Those pitchers who allow themselves to be unraveled frequently by errors might have flawed skills, which could easily be exposed even when backed by a flawless defense.

These were the leaders in unearned runs in 2010. The chart includes what percentage of the team's unearned runs that pitcher allowed, as well as the number of times opposing batters reached base via an error.

Greinke's numbers stand out. Yes, his Kansas City Royals did commit a lot of errors (121, sixth-most in the majors), but that he had the most opposing batters reach base via an error (17) yet committed only 12 unearned runs is actually a bit of a feat. That's 17 extra outs he should've recorded, and if you're buying talk that he got zero team support, there's another reason; the Royals were excellent at helping extend Greinke's innings. If the Milwaukee Brewers, who were a much more league-average defense than the Royals in 2010, support him with stronger defense, Greinke's ERA could be in for a significant drop. This isn't to say the Brewers' infield will help, see below, only that they may make fewer errors.

Conversely, Saunders' numbers are ominous, for a pitcher who had a so-so 4.25 ERA after coming over to the National League. Only one pitcher allowed a greater percentage of his team's total unearned runs -- Saunders' percentage combining his days with both the Los Angeles Angels and Arizona Diamondbacks -- and that was Mike Leake (32.4), and Saunders managed to surrender 19 unearned runs despite only 10 opposing batters reaching base via error. But that shouldn't really surprise you; Saunders' WHIP has been north of 1.40 in each of the past two seasons and he's as strong a bet for 200-plus hits as there is in the game. It doesn't really matter how accurate the defense behind him, because Saunders allows so many baserunners, his ERA is at constant risk of ballooning past 4.50.

Team defense

This isn't exactly the same as the previous section, unearned runs, because unearned runs occur only as a direct result of an error or passed ball. Defense, however, is about a heck of a lot more than merely errors and passed balls. Range -- a better measure of a defense's ability to convert balls in play into outs -- is every bit as important and arguably much, much more so. A defense can be accurate with the plays it makes, but that doesn't mean it's getting to the tougher plays, which, when made, result in greater team success. Perhaps there's no greater example of that than last year's New York Yankees; they committed the fewest errors in baseball (69), but in terms of both UZR (ultimate zone rating) and UZR/150, they didn't crack the top 10 (11th in each category).

Speaking of the Yankees, their shortstop, Derek Jeter, specifically has been criticized for nearly a decade for what has been considered mediocre-to-poor range. (I choose the phrase "what has been considered" only because Jeter has had a few seasons where his defensive metrics have been at least average.) Using the Jeter example, he's not especially sound on plays to his left, whereas a league-average or better shortstop might make a play Jeter wouldn't. The better defender might convert a few more tough plays into outs, or in some cases two outs (double play), and those extra outs can have a profound effect on a pitcher's ERA.

It's for that reason there are countless statistical tools out there to measure the impact of defense upon a pitcher's ERA. Two of my favorites are FIP (fielder independent pitching), and xFIP (expected FIP), both of which evaluate a pitcher's performance regardless of how his fielders performed behind him. The difference between the two: Whereas FIP includes a pitcher's home runs allowed in the formula -- (HR*13+(BB+HBP-IBB)*3-K*2)/IP, plus a league factor designed to put it on an ERA scale -- xFIP "normalizes" home runs, calculating instead based on the league average of home runs allowed per fly ball.

Pitchers whose FIP or xFIP vary greatly from their ERA might have experienced one of two things: particularly strong or poor defense, or particularly good or bad luck. That's why, when evaluating ERAs, it's smart to take FIP/xFIP into account. A caveat, however: Some pitchers do tend to be historically strong in FIP/xFIP despite it never resulting in a low ERA -- Ricky Nolasco being a prime example -- so it's also smart to consider a pitcher's FIP/xFIP history.

These were the 2010 leaders in both FIP and xFIP:

Francisco Liriano immediately stands out as a pitcher who appears to have performed better than his ERA last season, which is odd considering his Minnesota Twins were one of the better defensive teams in UZR and UZR/150 (sixth-best in each). Only Jason Hammel (+1.11) had a greater differential between his ERA and FIP on the negative side last season than Liriano, which helps explain how we're confident that Liriano's 3.62 ERA of a year ago should drop to our 3.44 projection for 2011 (with upside for even better than that).

Conversely, both Trevor Cahill (2.97 ERA, 4.19 FIP, 4.11 xFIP) and Tim Hudson (2.83/4.09/3.87) are nowhere to be found on these leaderboards, and that's exactly why you'll often see the label "regression candidate" applied to either. Both are low-strikeout, ground-ball pitchers, putting their success mostly in the hands of their fielders. That's not to say that neither has the ability to repeat 2010's sub-three ERAs, but their FIP/xFIP numbers show that pitchers with their style typically should be expected to finish with ERAs much higher. Sure enough, Hudson is projected with a 3.25 ERA, Cahill 3.57.

Strand rate

Also called left on base percentage, this measures a pitcher's ability to prevent runners he allows to reach base from scoring. Along with BABIP and home run/fly ball percentage, strand rate is one of the more popular measures of a pitcher's luck. A typical, league-average strand rate is generally about 70-72 percent; those who have numbers significantly higher might have gotten a few lucky bounces, while those with numbers significantly lower might have been struck by terrible luck.

Not to say that strand rates are always a sign of good or bad luck. Dave Bush, for one, is a pitcher who historically has struggled pitching out of the stretch, his .282/.335/.465 career rates allowed with men on base leading to a 68.8 percent career strand rate. Johan Santana, meanwhile, has a 78.5 percent career strand rate, thanks to .224/.285/.344 career rates allowed with men on base.

These were the leaders and trailers in strand rate in 2010:

There's Greinke again, on the "unlucky" side of the ledger. Here's what's odd about his 65.3 percent strand rate of 2010: Not only is his career number (72.5) more than 7 percent higher -- and well within range of the league average -- only twice in his seven big league seasons has he had a strand rate beneath 75.2 percent. Numbers like that have a tendency to even out over time, and if Greinke can bring his back into the low 70s, it's going to mean fewer earned runs on his stat sheet. Again, having a stronger defense supporting him should help.

Jonathan Sanchez, meanwhile, had one of the "luckier" numbers in terms of strand rate, his 79.5 percent more than 7 percent higher than his career number in the category (72.2). For a pitcher who averages 4.60 walks per nine innings during his big league career -- and 4.47 in 2010 alone -- Sanchez shouldn't be expected to repeat the effort, especially not with the defensive questions on the left side of his infield. If you're looking at him as a possible breakout candidate, thanks to his second-half surge, let that number help temper your expectations.

Bullpen support

One of the least discussed, and infrequently measured, factors that impacts ERA, a starting pitcher's bullpen support can be critical to his success. Fantasy owners might see a starting pitcher's final stat line in the box score on any given night, but what they might not see was that the pitcher departed with two outs and the bases loaded, only to see his reliever surrender a grand slam in the very next at-bat. Three of those runs are charged to the starter, a significant hit to his ERA. Even a small handful of extra inherited runners allowed to score by the bullpen over the course of a given season can taint an otherwise quality performance by a starting pitcher, so always consider whether such a starter might have been let down by the men behind him when evaluating his ERA.

Baseball-Reference.com tallies "bequeathed runners," or runners whom a starter leaves on base when departing; the chart below shows 2010's leaders in terms of percentage allowed to score, minimum 10 bequeathed runners.

Only one pitcher in baseball had his bullpen allow more of his bequeathed runners to score than Brian Matusz (12) last season, and that was Kevin Correia (13). Matusz's Baltimore Orioles had the game's sixth-worst bullpen ERA (4.44), but perhaps the offseason addition of closer Kevin Gregg, as well as a fully healthy season by left-hander Mike Gonzalez, might help in that regard. The impact of all of those runs was pronounced; had only half of those bequeathed runners been allowed to score, Matusz's ERA would've been 4.00, not 4.30. It's one of the many reasons we view Matusz as a potential breakout candidate, with a 3.73 projected ERA.

Conversely, Anibal Sanchez's bullpen allowed only three of his 25 bequeathed runners -- those 25 the 10th-most in the majors -- to score, making him an incredibly fortunate pitcher. The Florida Marlins, after all, allowed 30.4 percent of their bequeathed runners to score as a team, and had a 4.01 bullpen ERA that ranked them 17th in baseball. Winter additions like Ryan Webb and Edward Mujica might help, but Sanchez can't be expected to be so fortunate in 2011. Sure enough, we expect some correction to his ERA: He's projected for a 3.83.

Ballpark factors

This one's obvious. A pitcher's ERA is impacted by the venue he calls home, as bandbox ballparks lead to untimely home runs that inflate that number, while those who pitch in spacious venues can afford the occasional mistake without taking as much of a hit. Fantasy owners have long taken this into account, but for a specific measure of a ballpark's impact on ERA, adjusted ERA (or ERA+) can be a handy evaluation tool. What it does is calculates a pitcher's ERA assuming a neutral ballpark; anything significantly over 100 is considered good, beneath 100 bad.

These were the 2010 leaders and trailers in ERA+:

There's Buchholz again, his major league-leading ERA+ demonstrating how remarkable his season was despite what wasn't the most pitching-friendly of venues. You can argue that his other metrics make him a regression candidate -- he was among the 2010 leaders in highest strand rate, as seen above -- but at the same time his performance was somewhat remarkable, considering his Boston Red Sox's defensive metrics were mediocre and Fenway Park isn't the friendliest place for a pitcher. Buchholz's low strikeout rate (6.22 per nine) puts him at risk for a higher ERA in 2011, but it's numbers like his ERA+ and what should be a strong defense supporting him that kept his projected ERA at 3.35, instead of much higher.

Meanwhile, pitchers like Scott Baker and Jonathon Niese, who call pitcher-friendly venues their homes, had more disconcerting ERA+ numbers. Baker's number might have been partly a product of pitching through injuries, but all that does is demonstrate the need to closely monitor his progress during spring training. Niese, meanwhile, will always be helped by the spacious confines of Citi Field, keeping his ERA from soaring, but his skill set hardly makes him an ideal bet to rank among the leaders in the category.

Not that any one of these five influences should be expected to radically shift a pitcher's ERA in one direction or another, but they can, which is why instead of looking at that one category on the surface, you need consider what went into it. Remember, even for the most durable starting pitchers, one earned run can mean a 20th of a point in ERA or more; five earned runs can cost a pitcher as much as a quarter of a run in ERA (and often an ERA crown).

That's why, when evaluating pitchers, I place ERA lower on my priority list than categories like WHIP, strikeout and walk rates. That's not to say ERA is devoid of value -- you simply can't take it at face value.

Tristan H. Cockcroft is a fantasy baseball analyst for ESPN.com and a two-time champion of the League of Alternative Baseball Reality (LABR) experts league. You can e-mail him here, or follow him on Twitter @SultanofStat.