Why are we seeing so many perfect games?

Matt Cain’s perfect game Wednesday night means there have been five perfect games since 2009, which is also about a quarter of all perfect games ever. ESPN has referred to the “Era of Hurlers” and many have come to wonder how the era of offense has so quickly switched to the era of pitching, though it turns out we are in living in the era of both.

Though this seems like a contradiction, it’s actually the case that since the 1990s both pitchers and hitters have improved by working on things that actually matter for winning games, as opposed to forsaking home runs for average or seeing a walk as nothing catastrophic; Pitchers have been striking out more hitters and walking (slightly) fewer, while hitters have focused on hitting for power at the cost of increased strike outs. This has improved both sides since it turns out that striking out does not hurt a batter’s value all that much –certainly much less than must have previously been assumed – and hitting home runs helps it a lot, while pitchers are there to pick up the extra strikeouts – lowering their ERAs in the process – and focus on pounding the plate, putting the onus on the defense, since hurlers cannot control where a batter is going to hit the ball anyway, both of which lead to a higher WAR.










On the graphs above you can see what I’m talking about: a rising K% for batters with rising ISO on the left, and rising K/9 with falling BB/9 on the right. A curiosity worth mentioning is that even after batters’ ISOs fell (post-PEDs), their high K% rates persisted. This is enough for me to say that pitchers have figured out how to strike out batters at high rates and batters, regardless of steroid use, are either helpless or indifferent to it. That is, high strikeout rates are not a product of the steroid era.

It is, therefore – given the extremely high rates at which pitchers are striking batters out and the low rates at which they are walking them – not a coincidence that there have been far more perfect games in recent history than ever before.


(Note for the above graph: Remember that there have been only three seasons since the 2010 decade began)

To explain what I mean by this, I need to give a little information on how a perfect game happens. Sabermetricians are fond of referring to perfect games as dumbluck occurrences, as if they can happen to anyone at any time. Yet the list of pitchers who have thrown perfect games includes many impressive names, such as Cy Young, Jim Bunning, Sandy Koufax, Catfish Hunter, Tom Browning, David Cone, Randy Johnson, Mark Buehrle, Roy Halladay, and now Matt Cain. Indeed, very few of these pitchers “came out of nowhere” to throw a perfect game, and the most notable exception to this observation is Don Larsen, who is all the more famous particularly because he did “come out of nowhere.” That is, the popular perception that perfect games tend to be thrown by good pitchers is well-founded. Here’s why.

A perfect game is one in which there are no hits, no walks, and no errors, resulting in only 27 plate appearances. Now, since all I’m interested is the likelihood of a perfect game happening at any time during the year and not predictions of the chances of throwing a perfect game for specific players, my job is a lot easier. As a rough approximation to give an idea of how often a perfect game can be expected to occur, I calculated how many hits plus walks (I ignore errors) a pitcher could be expected to give up over 27 plate appearances. The lower this number is the more likely a pitcher will throw a perfect game. To do my calculation, I used a simple formula combining a pitcher’s K/9, BB/9, and batting average on balls in play (the percentage of balls put into play that go for hits) allowed. Again, the lower the number I calculated is (the number is made lower by batters striking out more, walking less, and getting fewer hits) the more likely a perfect game is to occur.


Though the graph above may look complicated, all you need to know is the blue dot is the average of my proxy for the likelihood of a perfect game (the lower the more likely) and that the red bars give an idea of the spread of likelihoods for various pitchers in the corresponding (again, the lower the more likely a perfect game). The most important thing to notice is the steep descent of the blue dots since 2007, arriving at the lowest blue dot and the lowest extending red bars of all-time (since 1970) in 2012. Meaning that due to the low walks rates and very high strikeout rates of modern pitchers, there has never been a situation where the occurrence of a perfect game has been more likely.

Here’s the summary: During the mid 1990s hitters began focusing on hitting more home runs and in the early 2000s pitchers began focusing on reducing walks and increasing strikeouts. Strikeout rates for pitchers rose all throughout the PED era, and continued to rise even after PEDs were banned, meaning that the improvements in pitchers’ strikeout rates are due to improvements in pitching, and not just to the changed approach of batters. Both batters and pitchers have become better since the 1970s, and one result of this has been the increased likelihood (and occurrence) of perfect games. Although batters have gotten better at hitting (BABIP allowed rose drastically to .300 in the 1990s and has since stayed there), walk rates have gotten so low and strikeout rates so high, that they wipe out the gains made by batters when it comes to the chances of throwing a perfect game; in other words, there are simply fewer chances per 27 plate appearances for a batter to break up a pitcher’s perfecto.

Augmenting this systematic shift in favor of more perfect games is the fact that elite pitchers excel in the factors that increase the likelihood of a perfect game (more strikeouts, fewer walks) to an even greater degree than average pitchers. The 2012 season will likely see the most pitchers ever to have a walk rate below two per nine innings. It is really not that difficult for a pitcher who averages less than two walks per nine to walk nobody over 27 plate appearances. And with 2012 likely to feature some of the highest 

K/BB ratios of all time, especially among the top twenty or so hurlers, it is likely that prior to the last four years or so, there has never been a more likely time to see a perfect game.

Yet, there is still much of a perfect game that comes down to luck, and that is why they are so rare. But it is likely not a coincidence that last night’s perfect game came from a pitcher with a very high K/BB (Matt Cain’s 6.00 K/BB ratio is second in the majors). The Nationals own Stephen Strasburg, at 5.00 K/BB, is very close behind Matt Cain. But even if Strasburg does not luck out on a perfect game, if the trends in hitting and batting described above continue – and my feeling is that they will, at the very least for a year or two more – then we should expect the perfect games (and no-hitters) to keep coming at historic rates. What a great time to be a fan.