Stephen Strasburg, Dazzy Vance and Context

Eric Seidmen wrote an interesting article last Thursday about Atlanta reliever Craig Kimbrel’s historic strikeout pace. So far, Kimbrel is sporting a blistering 42.7% strikeout rate (K%). Even for a relief pitcher in this era, that’s incredibly impressive. But one person who commented on the story noted that there was a non-reliever approaching the same level of whiff greatness (i.e. > 30% strikeout rate).

Nationals phenom Stephen Strasburg has thrown 182 innings in the big leagues and has struck out 32.5% of the batters he’s faced. No starting pitcher who lasted any significant amount of time ever finished his career with a strikeout rate higher than 30%. The closest  is Randy Johnson and his 28.5% strikeout rate. This season, Strasburg has a 33% strikeout rate. If he were to maintain that pace, he’d be the 10th starting pitcher in history to achieve the feat and would have the 23rd such season since 1916. But take a look at that list and you’ll note that the oldest instance came back in 1984.

The problem we run into with strikeouts — like many statistics in baseball — is that the playing environment has changed over time.

The average rate at which pitchers record strikeouts has jumped dramatically since 1916 (the earliest year we can calculate strikeout percentage). That year, the league-average starter had a 10.5 K%. Compare that to the current 18.6% rate this year, and we have a massive gap. Whether hitters are more prone to strikeouts, pitchers are simply nastier now, or some combination of environmental and structural changes to the game (e.g. how players are selected, technology, etc.), the fact is a strikeout in 1916 was rarer than one today.

Fortunately, integrating some context into the conversation is incredibly easy. We simply need to calculate a “plus” statistic for strikeout rate so that we can compare how much better than league-average an individual pitcher’s strikeout rate is in a given season. Here’s the formula for calculating what I will call K%+: [(Pitcher’s K% / League Average K%) * 100].

Similar to wRC+, a K%+ of 100 means that a pitcher’s strikeout rate was league-average*. A pitcher with a 125 K%+ would have a strikeout rate 25% better than league average, and a 75 would indicate a rate 25% worse than league-average.

So if we adjust all individual qualified starter seasons since 1916 in this way, which pitcher had the greatest single season in terms of strikeout rate? The one and only Dazzy Vance.

Vance posted a 21.5 K% in 1924, which ranks as the 404th-best strikeout rate in a single season. But back then, the league-average K% was a mere 6.9%. That means Vance posted a whopping 312 K%+. That season, Walter Johnson had the second-highest K% at 13.8%, which translates to a 200 K%+**.

In fact, if we look at a K%+ leader board, Dazzy Vance appears more dominant in terms of strikeouts than any other pitcher.

Vance has four of the top five spots on the list and six of the top 12. Of his 11 qualifying seasons, his 170 K%+ was his worst. The best non-Vance season came fromLefty Grove in 1926 (251 K%+). To add some additional context, Randy Johnson posted eight seasons with a K% of greater than or equal to 30% (most all time, double the number by Pedro Martinez). Here’s Johnson’s top 10 K%+ seasons, compared to Vance:

Johnson’s best season ranks 14th in terms of K%+; Vance had six seasons better than that. The point here isn’t to say that Johnson wasn’t that great (he was phenomenal), but to illustrate how much the changing environment impacts just how great today’s strikeout artists compare to those who played long ago.

So, getting back to Strasburg. Let’s assume he finishes this season with a 33% strikeout rate. As impressive as that would be, it would still only rank 129th historically in terms of K%+ — by far the lowest of the other 23 30%+ strikeout rate seasons we’ve seen from starting pitchers. Now, 129th out of 6,980 seasons is nothing to sneeze at. But it does illustrate the need to put the current strikeout successes that we are seeing into historical context. Strasburg is undoubtedly one of the most talented strikeout pitchers the game has seen. But he also is pitching in the most strikeout-friendly era of the past 96 years.

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*However, K%+ is not park-adjusted.

**If we had K% data going back further, Johnson would no doubt have been more of a force on the leader boards.