The Changing Reality of the Lefty Strike

You guys keep asking questions about FIELDf/x. You guys really want to get some information out of FIELDf/x. The unfortunate reality is that, right now, FIELDf/x is more of a concept than a tool, and on top of that, even if it were turned into something flawless, the data probably wouldn’t be made public. But you want some novel ideas or new presentations, like we all got out of our glimpse of HITf/x. And as much as it’s just commonplace now, don’t forget that PITCHf/x is amazing. So many fascinating projects, the instant PITCHf/x went public. It changed the way we all analyze. It changed the way we look at the game.

One of the first things that really blew my mind, personally, was being able to visualize the actual strike zone, as it’s called, and not as it’s supposed to be. We all had our ideas, but PITCHf/x allowed us to know, for fact. We could see which parts of the rulebook zone don’t get calls. We could see which parts outside of the rulebook zone do get calls. We could see that righties and lefties get different strike zones, and I couldn’t believe it when I saw the typical called strike zone for left-handed batters. There were a ton of called strikes leaking off the outer edge, some several inches from the plate. This has been established over and over again as a thing that happens, and those pitches are commonly referred to as lefty strikes. At this point many of us just take them for granted.

Which speaks certain volumes, since by definition none of those pitches should be called strikes. The strike zone is supposed to be over home plate, only. We have proof that umpires have been calling strikes off the plate against lefties for years. Maybe people raged against this early on, but now it’s just part of baseball. Those are pitches that just get called strikes, for whatever reason. Theories abound. Those are pitches that seem to give some rookies and young players fits. Fans like to half-joke that a given rookie knows the strike zone better than the umpire does, when the player lays off a called lefty strike.

I think a pretty good indicator that you’re a baseball nerd would be if you know about the existence of the lefty strike. Another good indicator would be if you make a habit of reading FanGraphs so I guess, hey, we’re all baseball nerds. As baseball nerds, we can also appreciate the significance of small trends in statistics. About that lefty strike, then.

I’ve written in the past that umpires, if nothing else, are getting more consistent overall. That is, home-plate umpires, with regard to balls and strikes, and the evidence suggests they’re calling fewer strikes outside of their zones, and fewer balls within them. Some of this could just be PITCHf/x getting better, instead of umpires getting better, but I think it’s probably both, with the majority having to do with the umps. And recently I wanted to more closely examine the nature of lefty strikes over time, during the PITCHf/x era.

The following wouldn’t have been possible without database help from Jeff Zimmerman. So, he did this article a solid. I created for the lefty strike an approximate box. The first step is isolating pitches against lefties, in each season. The next step is narrowing down to pitches between 1.5 and 3.5 feet off the ground. The final step is narrowing down further to pitches between the outer edge of the plate and the point 1.5 feet away from the center of the plate. Within this box are the overwhelming majority of lefty strikes. I wanted to know if things have changed at all over time since PITCHf/x was introduced.

Below, a table, with all the information you need.

Year	# In Box	Freq%	Swing%	CalledS%
2007	28699	N/A	42.1%	49.6%
2008	60652	19.8%	40.9%	48.4%
2009	65226	20.3%	40.9%	49.0%
2010	61068	20.2%	40.9%	48.1%
2011	61287	19.9%	41.9%	47.7%
2012	61997	19.9%	42.0%	47.4%
2013	61889	19.5%	40.4%	43.1%

In the first column, the season. In the second column, the number of pitches to lefties within the box. In the third column, the percent of all pitches to lefties within the box. In the fourth column, the swing rate at pitches within the box. In the final column, the rate of called strikes on pitches within the box, expressed as Called Strikes / (Called Strikes + Balls) * 100 and excluding pitches that were swung at. Data for 2007 is incomplete, that being PITCHf/x’s debut year.

As you can see, about one of every five pitches to lefties is thrown within the box. About two of every five pitches within the box are swung at. Used to be, about 49% of pitches taken within the box were called strikes. Since 2009, the rate has been dropping, and it dropped quite a bit between 2012 and 2013. Last year, just 43% of pitches within the box were called strikes, and while what we’re looking at is a fairly modest drop, it’s also significant and encouraging if you look at it in the right way. Or in almost any way.

Between the last two seasons, it’s a difference of about one strike per 51 left-handed plate appearances. Maybe that makes it seem even smaller. But it’s improvement, and you can never be unhappy with progress, and who’s to say how much further this goes? Just for illustrative purposes, here’s David Ortiz in 2009 and David Ortiz in 2013, with the lefty strike zone boxed off:

There are still lefty strikes in 2013 — quite a lot of them — but there are fewer, and most of them are closer to the plate. Umpires might be reigning it in a little bit, and to see any improvement is positive since it’s not like they have immediate access to any better technology on the fly. This suggests umpires themselves are getting better about policing the lefty strike zone, perhaps in response to people identifying the existence of the box in the first place. The first step toward betterment is awareness.

A lot more could be done here, and people could examine other parts of the zone, both rulebook and actual. And no matter how much human umpires improve, they’ll always be flawed and get a lot of pitches wrong, just because of the limitations of our own eyes and brains. We’ll never be able to compete with the machines, because we make the machines almost flawless. But as long as ours is a game judged mostly by human eyes, it’s more encouraging than discouraging to see a slightly better called strike zone take shape. They’ve gotten better, and they could get better still. Maybe the improvement isn’t close to good enough for your taste, but it is absolutely better than nothing, if only by literal definition. The lefty strike is still there, but it’s a little less there.