The Astros’ sign stealing scheme has gripped the baseball world. Like any good scandal, it comes with corruption, intrigue, and, in keeping with the times, it also has a whistleblower. What’s lacking, however, is clarity, both with regard to the extent of the scheme, not to mention the prevalence of ones similar to it throughout the league, and the impact it had on outcomes.
There have been several attempts to determine the degree to which stealing signs may have helped the Astros, but the findings have been both inconclusive and contradictory. That’s not surprising when you consider the complexity involved in doing such an analysis. In order to accurately determine the effect from the cause, it’s not enough to rely on correlation (i.e., every “bang” was followed by a home run). One must also know the “opportunity context”, which includes the other variables involved and the likelihood of outcomes under those conditions. Of course, as with any scandal, that doesn’t mean we can’t look for smoking guns.
In a recent article at the Athletic, some “eye popping” evidence was offered, suggesting that the Astros might have benefitted significantly from their sign stealing scheme. In particular, the article highlighted the teams declining strike out rates and suggested the Astros’ improvements were at “levels unparalleled in the last 100 years”. But is that really true?
MLB’s and Astros’ Strikeout Rates, 1962 to 2019
Source: fangraps.com and baseball-reference.com
To its credit, the Athletic article does link to another study showing that the altered composition of the Astros in 2017 augured for a strikeout rate improvement before the season even began (the team’s actual strikeout rate was only 0.4 percentage points lower than what Fangraphs predicted). But, roster makeup wasn’t the only variable that needed to be acknowledged, much less considered. Another pertinent contextual factor left out of the analysis was the current high strikeout environment. By relying on a comparison of the number of strikeouts, and not the percentage change in the strikeout rate, the findings exaggerated the degree to which the Astros cut down on strikeouts. Put more simply in mathematical terms, declining from two strikeouts per game to one is a much bigger relative drop (50%), than going from nine to seven (22%), even though the latter results in twice as many fewer strikeouts. As the chart above shows, both MLB’s and the Astros’ historical strikeout rate was already at or near all-time highs by 2016, so if the team was successful in executing a strategy to lower strikeouts, the result in terms of the number of events would likely be historic.
Largest Strikeout Rate Declines by Percentage
Source: fangraps.com and baseball-reference.com
When considered on a percentage basis (change in strikeout rate, not percentage point difference), the 2017 Astros still recorded a historically impressive strikeout decline. The drop of 26.1% (from 23.4% in 2016 to 17.3%) still ranks as the ninth largest by a team since 1914, but even when viewed as the most significant decline among a more recent top-10, the change doesn’t appear be as extraordinary as real numbers might suggest. So, it’s hard to argue that the team’s decline in strikeouts was mainly the manifestation of the sign stealing scheme. And, this argument is further complicated by the relatively modest snap back that occurred in subsequent years. After all, if steal signings was the main reason for the strikeout decline in 2017, shouldn’t the rates have reversed more significantly in 2018 and 2019?
Largest Strikeout Declines at Home, 1920 to 2019
Source: fangraps.com and baseball-reference.com
What about the team’s strikeout decline at Home? In 2017, the Astros struck out 242 fewer times at Minute Maid Park, but only 123 fewer times on the road. According to the Athletic, this represented the largest drop ever in strikeouts per game at home, but once again, when considering the change on a percentage basis, the distinction is lessened as three other teams jump ahead of the Astros in that ranking. Once again, it’s also worth pointing out the context, which in this case includes a preceding period in which the Astros not only had strikeout rates that were above the norm, but also were atypically higher higher at home than on the road. So, in this case, not only were the changes to the roster likely to lead to an overall correction, but a normalization of the Astros’ strikeout rate should have been expected to be even more dramatic at home.
MLB’s and Astros’ Strikeout Rates, Home and Away, 1962 to 2019
Source: fangraps.com and baseball-reference.com
Another comparison that fails to produce a smoking gun is the 2017 Astros’ home/road strikeout rate ratio, which, at 93%, doesn’t even rank among the top-1,000 lowest seasons since 1920. Incidentally, in 2016, the Astros ratio of 109.4% falls just outside the top-100 highest rates, suggesting that year was more of an outlier, but in the opposite direction. This also helps explain why the 2017 Astros strikeout rate saw greater improvement at home. In the previous year, the team’s hitters recorded a strikeout rate of 24.5% in Houston, which was the 19th highest home rate in MLB history. Once again, if the plan was to transition away from sluggers aiming for the cozy dimensions at Minute Maid Park, a significant decline in strikeouts, especially a home, would be expected.
Lowest Ratio Between Home and Away Strikeout Rates, 1920-2019
Source: fangraps.com and baseball-reference.com
The most compelling analysis done by STATS on behalf of the Athletic showed that the 2017 Astros had the largest disparity between its strikeout rate decline at home versus on the road. One could argue that if the new roster composition or a change in approach were the reasons for the team’s improved strikeout rates, such a large discrepancy shouldn’t exist in the current season splits. However, the strength of this argument is mitigated by the Astros’ anomalistic historical strikeout rates at home (depicted above) before 2017 and also weakened when viewed on a percentage point basis.
Largest Relative Y/Y Strikeout Rate Improvements, Home vs. Away, 1920-2019
Source: fangraps.com and baseball-reference.com
One final note, although the 2017 Astros did strikeout much less at home, the team’s offense was actually better on the road. In fact, Houston ranked next to last in terms of tOPS+ at home (compares the split to the team’s overall performance) and first in terms of road sOPS+ (compares the split to the league’s overall performance).
Home/Road Splits, 2017
Source: baseball-reference.com
Finding definitive evidence to suggest that the Astros benefitted from sign stealing as a team is hard enough, but what about the impact on individual players? Based on a few examples, it does appear as if there is a link between the decline in K rate and the “bang” rate (percentage of pitches in which a “bang” could be heard, as per data compiled by signstealingscandal.com). But, the inverse correlation is actually pretty weak (-0.19). And, when you try to craft a narrative, the strands become entangled. For example, Evan Gattis jumps off the page with a 41.3% decline in his home strikeout rate, but his road strikeout decline was a similar 37.2%. And, what about Jake Marisnick? He was the benefactor of the most bangs per PA, but his strikeout rate at home actually rose by 6%. That conclusively contradicts the theory, right? Well, not exactly. As it turns out, Marisnick’s strikeout rate on the road increased by 52.5% in 2017, so perhaps knowing so many pitches at home helped keep that increase in check? Marwin Gonzalez is another case that is difficult to explain. In 2017, his home strike rate increased by 2%, despite having the second highest percentage of “bangs” and seeing his road strikeout rate plummet by 33.9% (and then snap right back in 2018).
Strikeout Comparison Charts
Note: Bang rate is the percentage of pitches that were preceded by a banging noise as compiled by signstealingscandal.com. This does not include other forms of sign notification nor account for the fact that the lack of noise was itself a signal at certain times.
Source: signstealingscandal.com and baseball-reference.com
Logic doesn’t flow consistently when comparing how individual Astros performed at home versus the road and from one year to the next, but that’s usually the problem when trying to turn anecdotes into evidence. Because of the complexity involved, we will never know the extent to which the Astros sign stealing scheme aided their performance, but, we do know that they cheated. And, that alone should define their culpability, not how good they were at it.
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