Was Greinke's Streak Better Than Drysdale's?
Last week, Zack Greinke wrapped up a 38 consecutive scoreless inning streak, garnering him a Sports Illustrated cover, and the most attention a Kansas City player has received in quite some time. Greinke, the 25-year old righty who's been flying under the radar the past several years, made headlines by challenging the pitchers' version of Joe DiMaggio's 56 consecutive game streak.
But while Greinke's streak was impressive, surely it was not the quality of Don Drysdale's 1968 feat of 58 innings, which broke Walter Johnson's 55 year-old record and stood for 20 years on its own. Right? Perhaps... To test this, we'll try to calculate the probability of a typical "good" pitcher accomplishing both streaks.
Let's take a look at the two streaks:
Drysdale's streak of 58 innings started with a May 14th shutout of the Cubs at Dodger Stadium and he pitched 5 additional shutouts before letting up a run in the 5th inning against Philadelphia on May 31st. Greinke's streak of 38 innings started at the end of 2008 and continued through this year until he gave up an unearned run last week in the 5th against Detroit (he finally gave up his first earned run in the first inning of the following game).
On the face of it, it would appear that the Drysdale's streak was vastly superior to Greinke's, but let's look at the hitting prowess of each of the opponents they faced.
Drysdale made his run during 1968, The Year of the Pitcher. Greinke on the other hand made his during a relatively good hitting era (the stats in the above chart are the 2008 runs/game for Greinke's opponents). The average number of runs per game of Greinke's opponents was nearly a full run and a half higher than Drysdale's!
Greinke's opponents did however, play in slightly more favorable hitters parks than Drysdale's. When adjusting the teams' runs per game by their 3-year park factor, the weighted average of Drysdale's opponents scored 3.48 runs per game and Greinke's opponents scored 4.93 runs per game. This means that an average pitcher facing Drysdale's opponents would give up about 3.48 R/G, but that same pitcher facing Greinke's opponents would give up 4.93.
This however, still ignores where the games during the streak actually took place. Here Drysdale clearly had an easier go of it. Forty of his 58 innings were thrown at home, which increases his performance by about 5%, and only 18 innings came on the road, where the average player's performance decreases 5%. On top of that, his home games were played in the spacious Dodger Stadium. In the early years of Dodger Stadium, the park depressed runs by 16%, making things much easier for a hurler. On top of that, his road games were played in Houston and St. Louis, also both pitchers parks - depressing scoring by 4%. When you factor all of that in, the expected runs per 9 IP of a pitcher throwing those same innings drops from 3.48 to 3.00.
Greinke on the other hand didn't enjoy those advantages. Only 16 of his 38 innings came at home, making it tougher for him to complete his streak, while the park factors generally cancelled each other out. Overall, the expected runs per 9 IP went up from 4.93 to 5.03.
Since the streak includes earned runs and unearned runs, the proficiency of the defense also makes a difference (of course, defense is a factor no matter what, but I don't have the UZR for the 1968 Dodgers). In 1968, the average number of unearned runs allowed per team was about 14% of the number of earned runs. The Dodgers were slightly worse, giving letting in additional runs to the tune of 18%. When this is factored in, the expected R/G for Drysdale's innings increases from 3.00 to 3.08. The Royals defense was also slightly worse than average, increasing the expected R/G for his innings from 5.03 to 5.06.
The following chart gives the expected number of runs allowed per 9 IP for each game of both streaks, after taking into account the opponent, park, home field advantage, and defense.
Of course, these numbers are for the average pitcher. We want to calculate the probability that a good pitcher, like Drysdale or Greinke, would be able to complete the streak. Of course, a good pitcher would be expected to give up far fewer runs. The ERA+ numbers for both pitchers were around 125 (128 for Drysdale and 123 for Greinke in 2008) so it makes sense to use that as a benchmark. Dividing by the 125 ERA+ number, we would expect a good pitcher to give up 2.47 runs per 9 IP during Drysdale's streak and 4.05 runs per 9 IP during Greinke's streak.
Which Streak Was Better?
Using these numbers, and the number of innings in each successful streak, we can determine the likelihood that the same "good" pitcher could complete each pitcher's streak. First we have to translate those run per game averages into probabilities of scoring. I'm sure there's been work done to do this theoretically, but instead I used empirical data from Retrosheet courtesy of John Jarvis to estimate that the probability of pitching a shutout inning during Drysdale's streak was about .825 and the probability of pitching a shutout inning during Greinke's streak was about .745.
Using these numbers we can compute the probability of our typical "good" pitcher completing each streak. For Drysdale, the chances were (.825) ^ 58 = 1 in 70,000. For Greinke, the chances were (.745) ^ 38 = 1 in 72,000. So in fact, due to the far tougher environment, Greinke's streak was actually tougher to accomplish than Drysdale's!
Actually, the numbers are so close that you would have to conclude that both streaks were equally as difficult - the potential error in making our above estimates and assumptions are far greater than this tiny difference. Even so, to the average fan it probably comes as a shock that the two streaks are even in the same company - Drysdale's streak is a celebrated piece of history, while in 40 years Zack's streak is unlikely to be remembered by anyone other than Mrs. Greinke and a few die-hard Royals fans.
In any case, it illustrates the importance of considering the time and place of a player's performance. If the two players were competing in equal environments, there's no question that Drysdale's streak would be a far greater accomplishment (when both have a shutout inning probability of .80, the chances are 1 in 5,000 for a 38 game streak, 1 in 400,000 for a 58 game streak). But they weren't and as a result, Greinke's streak is actually every bit as impressive as the Hall of Famer's. So while he won't get the acclaim, here's one writer who wants to say congrats to Greinke for matching Drysdale's timeless accomplishment.