Originally written on The Nats Blog  |  Last updated 11/18/14

Last week I wrote an article about where the strike zone actually is for pitchers. Based on research by Baseball Prospectus I concluded that the strike zone is determined partially by the rules and partially by the pitcher. I wrote:

“Pitchers face something more complicated than a static box determined by the plate and the height of the batter. If a pitcher can hit the catcher’s glove with little error and do so in or “near enough” to the strike zone, he will get a strike. If he is inconsistent he loses the “near enough” region and possibly even parts of the strike zone if he is too wild. In effect, an inconsistent pitcher faces a much smaller strike zone.”

From Baseball Prospectus

Note how much  tighter Felix Hernandez’s zone is. This is ostensibly because his pitches are “all over the place”, meaning he is “inconsistent”.

I also noted that there seemed to be an increasing preference toward pitchers over the past three seasons.

The numbers on the y-axis can roughly be thought of as “the percentage of all strikes that were actually balls.” Using plate discipline data from FanGraphs (provided by Baseball Info Solutions), the outcome of every pitch (in the zone hit, out of the zone taken, etc) can be obtained. After doing so, it becomes clear that the number of pitches in the zone or out of the zone and swung at (i.e. strikes) by each pitcher is almost always different from the number of strikes actually recorded by the pitcher. This difference is what I refer to as the “strike deficit.”

The strike deficit has been increasing over time, as in more pitches outside the zone have been called strikes. Is this because umpires are systematically favoring pitchers or because pitchers are becoming more consistent? I don’t have anything to add to this right now, though I suspect someone else already has it figured out.

The strike zone for a batter

It seems unsurprising that hitters also influence the strike zone. Anyone who’s played baseball knows this. Even in high school and youth baseball umpires seem more deferential to power hitters and indifferent to everyone else. It seems like the same trend plays out in the MLB.

The chart on the left illustrates the magnitude of benefit hitters have received from umpires. Those ludicrously tall bars on the right of that chart are Barry Bonds who was so good from 2002-2004 that his balls, too, were strikes. The fellows getting screwed on the left are, inexplicably, several 2007 Angels.

The chart on the right illustrates the spread of the strike deficit. First, it looks pretty “normal” as in following a normal distribution. The position of each player, however, is not random.

Here are all qualified hitters from 2002-2011 partitioned by the percent of strike deficit. The top 5% of hitters who benefitted the most from “ump bias” are clearly better hitters than the bottom 5%. I am guessing their hitting skills preceded their tightening strike zones.

Barry Bonds’s “Good Eye”

In 2002-2004 Barry Bonds had the three highest walk percentages of all time. In 2004 he walked 37.6% of the time he came to the plate. That year 21% of his strikes were actually balls. In 2002 and 2003 that number was 12%. These are by far the highest numbers of all time.

The rest of the top ten seasons are from hitters you would be hard-pressed to describe as “Ray Mendoza.”

To see the effect of the strike zone hitters such as this enjoy, observe Albert Pujols’ 2008 zone:

And note the large number of balls called low, inside-and-low in particular, and that one straight down the middle of the plate. There are also very few strike outside the zone.

Bad hitters

For some reason, of the eight hitters to get screwed the worst from 2002-2011, four of them are Angels and all of them are from 2007.

I really have no idea why this is the case. The Angels might be there because they faced particularly good catchers and/or pitchers, as most of the Angels players experienced a decrease in strike deficit that season.

As for why 2007 was so bad, I’m not really sure. 2007 seems to have been a pretty neutral year for hitters overall, so maybe somebody had severe issues with Reggie Willits.

What’s going on?

Hitters, too, can influence the strike zone.  The hitters getting screwed are bad and the ones getting helped are good.

But these are general trends, not rules. There are many power hitters and many contact hitters not being influenced one way or the other. I have also not disentangled the effect of the catchers or pitchers they face.

But it does seem likely that very good hitters get a level of “respect” that overrides the pitcher’s influence. For everyone else, they seem to be at the will of the pitcher. Or at least that’s my best guess


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