May 20, 2013

Pebble Hunting

Extreme Strikeout Matchups

by Sam Miller

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On Sept. 18, 2011, Justin Verlander faced Chris Carter for the first and only three times to date. It went about how you’d expect, as Carter

struck out

three times

and that was that. A batter who strikes out more than anybody, and a pitcher who strikes out more than (nearly) anybody, should lead to a lot of strikeouts.

Max Scherzer, over the past two seasons, has struck out a higher percentage of hitters than Verlander, or any other starter in baseball. Last week he faced the Astros, who have struck out more than any team in baseball this year. The entire team has struck out in 26 percent of its plate appearances, which is two percentage points higher than Preson Wilson’s career rate. I, like you, don’t know why I chose Preston Wilson, but there you go. Okay, better: Justin Verlander's strikeout rate in the past two seasons is 25 percent, and that's the fifth-highest rate among starters (minimum 200 innings), and it's lower than the Astros' hitters. 

So when Scherzer faced the Astros last week, and the week before, you’d have expected big things. But Scherzer struck out eight in eight innings the first time, and seven in seven innings the second. His rate was lower than his rate against the league overall. Carter struck out twice in five trips. And this all made me wonder how many Scherzer should strike out when he faces the Astros, and how many times Carter should strike out in five trips against Scherzer, and whether there are any larger implications for the future of baseball, and so the second question and a little bit of this third question are what this is.

The answer to the second question, about how often Scherzer should strike out Carter, brings up Log5. Log5, which has a Wikipedia page, is a formula devised by Bill James to determine how often one team should beat another team, based on each team’s true winning percentage. With some tweaks, it can be used to calculate expected results for batter/pitcher matchups. So when a pitcher with an above-average strikeout rate faces a batter with an above-average strikeout rate, the likelihood of a strikeout is higher than both players’ typical rates.

Scherzer has struck out 30 percent of batters over the past two seasons, and Carter has struck out 34 percent of the time over the past two seasons, and the league average is a bit below 20 percent over the past two seasons, so according to Log5 Scherzer should strike Carter out 47.5 percent of the time.

Going beyond Carter, we can look at the 10 hitters who strike out the most (or have, in the past two seasons; we’re talking about observed strikeout rates, rather than “true” or regressed strikeout rates) and how they would do against Scherzer, as far as making contact:

Hitter	Scherzer
Carter	47%
Dunn	47%
Howard	45%
Salty	45%
Maxwell	44%
Alvarez	44%
Napoli	44%
Stubbs	43%
Arencibia	43%
Moss	43%

But Scherzer is only the best strikeout pitcher among starters. Craig Kimbrel strikes out nearly half the batters he sees, as it is. If he were facing the 10 dudes above:

Hitter	Kimbrel
Carter	66%
Dunn	65%
Howard	64%
Salty	63%
Maxwell	63%
Alvarez	62%
Napoli	62%
Stubbs	62%
Arencibia	62%
Moss	62%

But this is just theoretical. What actually happens when the most strikeout-prone hitters face the most strikeout-enthusiastic pitchers? A lot of strikeouts!

I looked at the 10 hitters above, and how they have done against the top five strikeout starters and the top five strikeout relievers over the past two seasons. That’s Scherzer, Yu Darvish, Stephen Strasburg, Clayton Kershaw, and Verlander; and Craig Kimbrel, Aroldis Chapman, Kenley Jansen, Jason Grilli, and Ernesto Frieri. In all, they’ve produced 165 matchups, and those matchups have produced 82 strikeouts. On the extremes, Pedro Alvarez is 0-for-6 with six strikeouts against Clayton Kershaw. Brandon Moss, meanwhile, has whiffed just once in six tries against Yu Darvish. That’s the closest thing to an extreme on the contact side, because basically everybody strikes out a ton in these scenarios.

The theoretical and the actual match up fairly well, though the difference is intriguing. If we apply the Log5 prediction to each matchup, we should end up with 74 strikeouts, not 82. All five starters have struck out more than they “should” have. Eight strikeouts isn't a lot, and 11 percent above expectations isn’t a lot. But strikeout rates also stabilize very quickly for hitters—100 plate appearances, Derek Carty once found—and if there’s not nearly enough here to say anything is up, there’s at least enough to generate a hypothesis and halfheartedly commit to looking into the issue further. So here’s a hypothesis: When a pitcher’s strikeout ability goes up, and a hitter’s strikeout rate also goes up, the resulting increase when the two match up will be even greater than expected.

When people talk about the reasons strikeouts are going up leaguewide, theories address both sides of the ball. Pitchers are better at striking batters out because they throw harder, throw cutters, face fewer batters at a go, have better catchers framing for them. Hitters are striking out more because they no longer fear the stigma of the strikeout, or because they’re swinging for the fences on two-strike counts. Let’s say all those things are true, and continue to be true, and strikeout rates continue to go up. Well, if the hypothesis turned out to be true, we would expect strikeouts to really continue going up, spurred on by the K-on-K matchup effect.

But that’s just a wholly untested hypothesis.

Incidentally, if you do the same exercise for the lowest-strikeout hitters and pitchers, there’s also a small surplus of Ks compared to expectations: 14, instead of an expected 11, in 217 plate appearances. If you do that exercise, you also find out that Derek Lowe against Marco Scutaro should lead to three strikeouts every 100 plate appearances, or 1/26th as many strikeouts as Carter against Kimbrel. Baseball might seem repetitive to the casual or burnt-out fan. But watch closely, and boy oh boy does this sport contain multitudes.

Sam Miller is an author of Baseball Prospectus. Follow @SamMillerBB
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