In part one of the "Knuckleball Hangover" series, we saw that Major League batters demonstrated a decrease of approximately six points of batting average and twelve points of wOBA the day after facing a knuckleballer. We suggested that if a hangover is real, then managers might use it by placing high-strikeout pitchers after knuckleballers in the rotation — taking advantage of batters whose pitch identification routine was recently jarred by trying to follow the atypical, fluttering movement of knuckleballs.

In part two, we explored the knuckleball’s effect on swing angles. We theorized that batters might adjust how they swing in order to make better contact with the fluttering knuckle movement, and that the adjustment may linger for the next game’s first few plate appearances. We found that, somewhat emphatically, to not be the case.

With evidence for a hangover dwindling, part three explores plate discipline data to see if perhaps hitters expand or become unsure of their zone post-knuckle matchup. To examine this we will compare three key sets of data. First, MLB-wide plate discipline numbers. Second, plate discipline data for the majors' two predominant knuckleballers. That should give us a baseline for both MLB and MLB versus the knuckleball.

A (not so) quick aside before we jump in, though. There’s some really interesting research being done on visual conditioning/training and its effects on hitters’ plate discipline. Pioneered by researchers based out of the University of California-Riverside — and first reported by, to my knowledge, BtBS's Chris Teeter — this research looked at batting statistics for the players in their proprietary training group before the 2012 season and after 2013, prior to which they underwent training at UCR (emphasis mine):

"They focused on strikeout rate (K%) and Bill James' runs created (RC) metric. The logic for choosing these metrics was that seeing the ball and identifying good pitches to hit would require good vision and familiarity, and one might expect that improved vision would lead to greater positive results. They found that K% for the trained UCR players decreased from 22.1% in 2012 to 17.7% in 2013."

I mention this not merely because it’s interesting, which it is, but because it demonstrates that there appears to be clinically verified precedent for what we’ve been searching for in this series. Visual games — and sometimes I forget baseball is a game — affect changes in our brains, our ability to perform tasks from simple to complex (such as identifying the spin rate of a ball moving 95 mph from just 60 feet 6 inches away). If facing a knuckleballer is a specific type of visual game, one that runs contrary to the game’s usual protocol of mid-90’s fastballs, then it’s scientifically reasonable to think there may be a lasting effect.

But, here’s where I immediately argue against myself: If you read the whole journal article behind the UCR study, you’ll see that a major question regarding the efficacy of the training is its duration. In other words, yes visual games can affect lasting neurological change and performance enhancement/deterioration but for how long?

(An aside within an aside: The "Home Run Derby Hangover" to my mind has been disproven.)

At last, to the data.

First, let's compare the MLB O-Swing rate to that of R.A. Dickey and Steven Wright over the past few seasons. Implicit in the hangover assumption is that batters chase pitches out of the zone a lot when they face knuckleballers, on bail out swings, unsuccessful check swings, and generally bad swings. So, I figure Dickey and Wright should post a higher O-Swing rate. Well…

It turns out that isn’t true. In every year (except marginally versus Dickey in 2015) hitters chase more pitches out of the zone against standard repertoire pitchers than versus the knuckleballers. This, to me at least, felt counterintuitive at first. We’ve all seen GIFs or video of a batter looking absolutely ridiculous chasing a knuckleball. But it actually makes sense. Fastballers and pitchers with a more standard pitch repertoire simply don’t miss the zone as badly as Wright or Dickey. Major league hitters do not often swing at a ball bouncing well in front of home plate or flying past the catcher. But they will chase high heat just off the outside corner or try to fight off a down-and-in slider on two-strike counts that’s close enough to be worrisome.

So if batters do not chase and miss more, maybe they produce significantly lower contact in the zone.

This chart should make you say, "ehh." Yes, contact in the zone is lower, but Wright and Dickey together have a Z-Contact rate of roughly 80 percent compared to MLB’s roughly 85 percent. The discrepancy is neither pronounced enough or consistent enough to give credence to the theory that batters’ rhythm is so disturbed by facing the knuckleball that recovery takes a game or two.

Before we move on, to drive home the lack of pro-hangover evidence in plate discipline data, here is the SwStr rate for MLB and for knucklers.

Some years the knucklers win, some years they don’t.

Let’s put a bow on it. Despite our Knuckleball Hangover theory seeming plausible prima facie, there is exactly zero evidence of it in swing angle data or plate discipline data. Whatever trouble batters are caused by the visually jarring experience of facing the knuckler, they appear able to shake off quickly.

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Steven Demmler is a contributing writer at Beyond the Box Score. You can reach him, if you dare, on Twitter at @sedemmler.