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.

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Jeff made Lookout Landing a thing, but he does not still write there about the Mariners. He does write here, sometimes about the Mariners, but usually not.

22 Responses to “The Changing Reality of the Lefty Strike”

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  1. Paul Clarke says:

    So there’s hope for Dustin Ackley yet.

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  2. olethros says:

    What the fuck happened between 2007 and 2008 to cause the number of lefty strikes thrown to more than double?

    Also, looks like hitters were aware of the lefty strike, and haven’t quite caught up to the reduction in number of them called. Look for that swing % to drop over the next couple of years.

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  3. mario mendoza says:

    So that’s catcher’s perspective, against both handedness of pitching?

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  4. ettin says:

    So this makes me wonder about overall changes in league walk and strikeout numbers? Is this change significant at all to the bigger picture? I believe FanGraphs has posted some of this information in previous articles but if an update is available that would be interesting (maybe?)!

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  5. Johnhavok says:

    Is there any real difference in the number of called “lefty strikes” that are thrown by LHP vs RHP?

    My thinking here is that if a LHP is throwing to the ouside of a LHB, the ball leaves that pitchers hand already on the inside part of the plate but finishes on the outside which may cause the ump to think it crosses home plate in the strike zone, rather than out in front of the strike zone.

    On the flip side, for a RHO they would realease the ball already outside to a left batter, and if it also finishes there, it’s easier for the ump to see that it probably never crossed the plate in the strike zone.

    Of course by this logic, you might expect to see the same type of extended Strike zone to the outside of a RHB when facing RHP, but not so much facing LHP.

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    • payroll says:

      I wonder if its the exact opposite. For RHPs, umpires setup on the inside corner and will see the initial trajectory of the pitch clearly, but will have to estimate the final 20 feet or so, when a RH fastball will be running further away from the plate. The opposite would be the case for LHP fastballs – their pitches would appear to head further outside than where they actually end up, due again to the final 20 feet of arm side run.

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      • paperlions says:

        I used to think of this as an effect of where the ump sets up as well, but now I wonder if it is just an effect of catcher handedness. I never realized how much umpire calls are affected by framing, in part, because I figured that umpires decided if a call was a ball or strike before a catcher caught it and that the umps probably couldn’t see the glove very well from where they were anyway….but now, knowing how much framing affects calls, I think it is simply that all catchers are right handed, so the “lefty strike” is to the catcher’s glove side, which makes it look better when he catches it….as opposed to the other side of the plate which would require the catcher to reach across his own body (or to set up way off the plate).

        So…that is my explanation, more effects of framing.

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  6. arch support says:

    Great article, Jeff. I’ve been fascinated by the difference between righty and lefty strike zones since I found out about it. I like to try to think about why there would be such a difference.

    One reason I thought of (I’ll let others debate whether it’s compelling) is that before Pitch F/X, the only tool an umpire could use for review of his strike zone was game footage. And game footage of pitches thrown is (almost) always filmed from over the pitcher’s right shoulder; that is, the camera’s view is usually from left-center field. So in review, the umpire would always have a biased perspective not from his own eyeballs, but from the camera angle. Pitches off the plate to righties look a little more obvious from this angle than pitches off the plate to lefties.

    So my thinking is: (1) ump calls pitches during games, (2) ump reviews game on video afterwards, (3) camera angle gives a relatively clear view of outer edge of plate to righties, but a muddled view of outer edge to lefties, (4) ump’s correct calls of outer edge to righties is reinforced while his calls of outer edge to lefties are not as clear, (5) the margin for error on the outer half against lefties remains bigger the next time he calls a game.

    Maybe this is putting the cart before the horse though: the ump is still calling the game from behind the plate and should get roughly the same view against righty and lefty batters. But if my thinking is correct only the mistaken calls against righty batters are caught (in the off-angle video review) afterwards and so the mistaken calls against lefties are allowed to persist through the next game because the ump doesn’t know he’s making them.

    This will all be moot with Pitch F/X being a better tool to evaluate strike zone calls. But still I’m curious to know what others think.

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  7. james wilson says:

    Is the lefty strike the same for RH and LH pitchers? I visualize the zone being expanded by lefty sliders and fastballs coming crosswise by the plate.

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    • I actually seem to recall the opposite — I think the lefty strike mainly exists for RHP vs. LHB. Unfortunately I haven’t been able to produce a link over a few minutes of research. I think it would have something to do with catchers setting up more outside targets with RHP.

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  8. Westside guy says:

    Looking at the numbers… while one can definitely convince oneself there’s a trend, we won’t really know if 2013 is an indication of real improvement – or just an outlier – for another year or two. There’s just not enough data yet to say 2011-2013 is definitely a trend.

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  9. Tom says:

    Jeff – how big a deal is the position on the rubber?

    While seemingly small, it can be a 24″ difference (more if you consider a left handed vs right handed arm slots?) and when you consider the average pitcher releases the ball at about 54-55ft (I think) does the ‘angle’ of the ball impact the call. Are umps calling the front of the plate or any part of the plate?

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  10. Nivra says:

    I found this article very illuminating:

    It doesn’t look like the strike zone is unfair for LHB, if anything, RHB have to deal with a 2% larger strike zone than LHB. The strike zone simply shifts towards the catcher’s left arm by 0.12 ft when a LHB is at the plate. For RHB, the strike zone is off-center towards the catcher’s left arm by .04 ft, and for LHB, the strike zone is even further off-center by another .12 ft.

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  11. Luke says:

    Great article. Question – has there been any noticeable change in stats for LHBs that would correlate with the lefty strike no longer being called? That is, did LHBs walk more frequently and strikeout less frequently in 2013 than in 2007-2012?

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  12. BurleighGrimes says:

    I sometimes joke that the lefty strike — or rather, a complete inability to adjust to the lefty strike — has killed Ike Davis’ career. Of course, it could just be that he’s kinda not that good of a hitter.

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  13. Jon Roegele says:

    Nice work Jeff. I’m looking at this topic in the THT Annual this year, how the strike zone has changed in the PITCHf/x era.

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