It's been surprising to me, given the profusion of new pitching statistics (FIP, VORP, Component ERA), that we haven't seen an expression of ERA or ERA+ that adjusts for leverage, weighing runs allowed in high-leverage situations more and runs allowed in low-leverage situations less. The data is available in the game logs at Baseball-Reference.com, but aggregating the data would be a tedious exercise. Fangraphs.com aggregates the data on a seasonal basis in the WPA, WPA/LI and Clutch statistics, but expresses the statistics in terms of incremental games won or lost rather than adjusted ERA.

Fangraphs calculates "Clutch" by subtracting WPA/LI, which aggregates the unleveraged increase or decrease in win probabilities associated with each plate appearance against a pitcher, from WPA, which also aggregates the win probabilities but assigns a leverage factor to each event based on the game situation (score, inning, base and out situation). Generally speaking, a pitcher with a positive Clutch factor performed better in high-leverage situations relative to his overall seasonal performance, or declined in performance in low-leverage situations relative to his overall seasonal performance, or some combination of the two. A better performance in high-leverage situations means that the incremental outs the pitcher got in high-leverage situations count for more than an average out (i.e., an out obtained in a game situation with a leverage factor of 1.0). A worse performance in low-leverage situations means that the incremental runs the pitcher allowed in low-leverage situations count for less than the average run (i.e., a run scored in a game situation with a leverage factor of 1.0).

The significance of the Clutch statistic should be obvious: not all runs allowed (and runs prevented) are equal. For example, the run surrendered in the bottom of the ninth of a tie game should be counted differently than the run surrendered in the bottom of the first inning after the visiting took a six run lead in the top half of the inning. ERA and ERA+ count each run the same, notwithstanding that the two runs I used as examples are likely to have had hugely disparate impacts on the outcome of the game. The advantage of expressing the number of leverage-weighted runs allowed as a variation on ERA should also be obvious: most fans will not know whether a Clutch factor of 0.74 is merely above average, or very good, or a spectacular achievement, but fans know how to compare a 116 ERA+ to a 135 ERA+.

It turns out that a Clutch factor of 0.74 - meaning that the pitcher's clutch performance was worth 0.74 wins for the season - is very high. A Clutch factor of 2.0 in a season is truly spectacular, and 3.0 or above exceedingly rare. Curt Schilling was a spectacular clutch performer in 2001, improving on his usual performance that year by 30% with runners on, by 48% with runners in scoring position and two-out, and by 20% in "late and close" situations. These spectacularly clutch performances translated into 2.03 incremental wins for Schilling as measured by win probabilities added. But if one expresses this same statistic by adjusting his ERA and ERA+ to reflect not only how many runs he allowed, but the impact of these runs given the game situation, what happens to Curt's 2.98 ERA and 157 ERA+ for 2001?

Leverage-adjusted ERA+ (or "LevERA+) is calculated by expressing the 2.03 wins Curt added by virtue of his clutch performance in terms of the equivalent number of runs. The concept of expressing wins in terms of equivalent runs is a common one in sabremetrics, although the appropriate win-to-runs conversion factor is difficult to calculate and varies depending on the league scoring level and "park run environment". Fortunately, Fangraphs has already calculated the conversion factor for us, and it can be found simply by dividing RE24 by REW (here's the Fangraph glossary that describes these two stats). Curt's RE24 for 2001 was 50.87 and his REW was 5.09. That means the appropriate win-to-runs conversion factor for Curt in 2001 was 50.87/5.09, or 9.99 (which is a fairly typical conversion factor in today's game). Multiplying Curt's 2.03 Clutch factor by 9.99 reveals that Curt's clutch performance was the equivalent of allowing 20.28 fewer runs than the 86 runs Curt allowed in 2001, or 23.58% fewer runs. Reducing Curt's earned runs allowed by the same 23.58% results in a figure of 65 leverage-adjusted earned runs (as compared to Curt's actual 85 earned runs in 2001). That means Curt's LevERA in 2001 was 2.28 and his LevERA+ was 205.

This is an extreme example, of course, because a Clutch factor of 2.03 for a season is extremely high. Most pitchers will have a Clutch factor much closer to 0 (that is, they were neither "clutch" nor "anti-clutch") and accordingly a LevERA+ that varies very little from their ERA+.

Just to give a further idea of how extreme Curt's 20 run Clutch improvement was, consider that since 1974 (the date from which the Clutch stats are available at Fangraphs) the largest career Clutch improvements and declines measure less than 100 runs. Curt, oddly enough, had a career Clutch factor of negative 5.26, which translates into 53.4 more runs and 50.75 more earned runs over his career. Again, that may not sound like much but it moves Curt's career ERA+ of 127 to a 122.1 LevERA+. That's still excellent, of course, but it's a difference to which most fans, and certainly most sabremetrically inclined fans, would attach some significance.

Another HOF aspirant with a significantly negative Clutch factor is our old buddy Bert Blyleven. Bert's Clutch factor for the first four seasons of his career - '70 to '73 - are not available, but it can be estimated on the basis of the leverage statistics at Baseball-Reference.com that Bert's Clutch factor for those four years would be slightly negative (very negative in '70, very positive in '71, mildly negative in each of '72 and '73). Let's assume for purpose of calculating career LevERA+ that his Clutch factor was precisely zero for his first years. That leaves Bert with the -3.88 Clutch factor he accumulated from '74 to the end of his career. That translates to 37.12 more runs and 33.48 more earned runs over his career, making Bert's career LevERA+ 115.9.

Here are the top 25 LevERA+'s among pitchers with 2000 or more innings pitched since 1952:

Guidry, Appier, Tudor, Palmer and Santana had the largest increases over ERA+. Maddux and Brown had the largest decreases.

There were three pitchers who ranked in the top 15 in ERA+ but not in LevERA+: Schilling, Smoltz and Mussina. Schilling had the largest drop (127 ERA+, 122.1 LevERA+). Smoltz dropped from a 125 ERA+ to 122.4 LevERA+. Mussina dropped from a 123 ERA+ to a 122.4 LevERA+.

In evaluating levels of run support provided to pitchers, increasing attention has been focused on run distribution and the potential that an adverse run distribution can make a pitcher's run support look better than it really was. A pitcher whose run support as measured by average runs/game scored by his team in his starts may have really received relatively poor run support because he received a very large number of runs in a small number of games, or had a concentration of games at the both the low-end and high-end of the spectrum. Although these kinds of adverse run distribution situations can (and do) occur within seasons, it is very unlikely that the phenomenon could persist over a lengthy pitching career, and I've seen no data that suggests that any pitcher in fact suffered from adverse run distribution over the course of his career.

Very little attention has been paid, however, to the distribution of runs allowed by pitchers, despite the fact that certain pitchers have exhibited distinct tendencies to pitch differently in high-leverage and low-leverage situations. Unlike distribution of run support, adverse distribution of runs allowed is far more likely to persist over a career because of the potential that a given pitcher possesses the tendency to pitch better or worse in high-leverage situations (or pitch better or worse in low-leverage situations, or some combination of the two). LevERA+ is a measure of the impact of the distribution of runs allowed by a pitcher. It reveals that certain pitchers, like Bert Blyleven, contributed to their own mediocre W-L records by performing relatively poorly in critical situations, and it reveals that other pitchers, like Ron Guidry, produced spectacular W-L records not only because of superior run support but because of their superior performance in critical situations.