Butterflies are not bulletsby John Walsh
November 27, 2007
Butterflies aren't bullets. You can't aim 'em—you just let 'em go.
— Charlie Hough
When I first started looking at the Pitch f/x data, data that gives us an unprecedented amount of information about every single pitch that it tracks, one of the first players that sprung to mind, one of my favorite players of all-time, was Boston's Tim Wakefield. You see, Wake is the only pitcher in the majors who throws the coolest, neatest, quirkiest, most unpredictable pitch in existence: the knuckleball. Now that we have over 1000 of Wakefield's pitches recorded by the Pitch f/x system, we can get a pretty good look at the knuckleball.
The strangest (and greatest) pitch
The knuckleball is different from all other pitches in many ways. First of all there is speed, or lack thereof: the knuckleball is one of the slowest pitches thrown on a major league ball field. It's not necessarily the slowest—Tim Wakefield's curveball is slower than his knuckler, but we'll get to that in a minute. Another unique characteristic of the knuckleball is the unpredictability of its movement. Nobody knows where it's going to end up, including the pitcher. And because of its erratic and unpredictable motion, I believe it's the only pitch that is not located: the knuckleball pitcher does not aim for a certain part of the strike zone, he just, as famed knuckleballer Phil Niekro put it, throws it at the catcher's mask and cheers for it on the way in.
There are other aspects that set the knuckleball apart: it's hard to catch; batters, when they do hit it, tend to make poor contact (knuckleballers seem to be somewhat free of the constraints posed by DIPS theory); there is no platoon split for knuckleball pitchers (or at least it's much smaller than the average split), and so on.
I suppose one of the most appealing things about the knuckleball to Joe Average is that it doesn't take a huge guy, with legs like Greek columns and million dollar arm to throw an effective knuckler. Just about anybody can learn to throw a knuckleball of some sort (even Wade Boggs), although, clearly, very few can learn to control it to the degree necessary for it to be a useful major league pitch.
Getting the breaks
So, just how does a knuckleball break? We've all heard the stories about knucklers doing incredible things and obviously they do. Now, with the pitch data available from mlb.com, we can begin to see what is really going on.
The chaotic glory of the knuckleball is best shown with the movement plot that I've used in the past. This type of plot shows the vertical and horizontal movements of a pitch relative to a hypothetical spinless pitch. These "movements", which are caused by the spin that is imparted to the ball by the pitcher, are useful, along with pitch speed, in identifying the different pitch types.
Now look at what Wakefield's pitches are doing: the knuckleball is that huge splotch of green points that don't seem to have a consistent break at all. They tend to break in any direction, or perhaps not at all. Crazy. Well, we all knew that the break of the knuckleball is unpredictable, but seeing this plot really drives the point home, doesn't it?
As you can see, the large majority of Wakefield's pitches are knuckleballs, but he does throw a, ahem, fastball (red points, 75 mph) and a very occasional curve (blue points, 60 mph). As we'll see shortly, Wakefield generally avoids these secondary pitches, unless he's behind in the count.
Another curious thing about the knuckler is that it changes speeds—by itself! A typical pitch loses about 10% of its original speed while on its way to the plate. The knuckleball also loses about 10% of its speed on average, but the variation from pitch-to-pitch is larger than for other pitches. As an example, the plot on the right shows the percent loss in speed for Wakefield's knuckler (green points) and for Sabathia's curve (light blue). So, the knuckleball is not only dancing left and right, up and down; it's also speeding up and slowing down as it comes into the batter!
In truth, the variation in speed is small in absolute terms: the spread in the average velocity (which is what matters to the batter) is only around 2-3 mph. Still, perhaps when you're putting all your concentration into following the dancing floater as it comes in towards you, the variation in speed is one more thing to worry about.
A loss of tactics?
Before a "normal" pitcher throws a pitch, he and his catcher must make a couple of choices. They must agree on the type of pitch and the location. Fastball in, slider away, split in the dirt, that kind of thing. They make these decisions based on several factors: who is batting, the count and number of outs, the score, what pitches are working for the pitcher that particular day, etc. This choice of pitch is a kind of cat and mouse game between pitcher and batter: the batter tries to anticipate what the pitcher will throw and the pitcher in turn tries to figure that out and throw something different.
When Tim Wakefield is on the mound, all of those tactics go out the window. Well, most of them, anyway. About 80% of Wakefield's pitches are knuckleballs. There really isn't any element of surprise, except for the surprise of seeing a pitch seem to defy the laws of physics—the batter doesn't try to guess what the pitcher is doing and the pitcher isn't trying to outsmart the batter. Wakefield just throws the knuckler right down the middle, 80% of the time. He's content to let chaotic air flow, or God, fool the batter and not worry about pitch selection or location.
Think about that for a minute: with the knuckleball, the whole battle between pitcher and batter is vastly simplified. You ever hear anybody say that Doug Mirabelli, who is Wakefield's personal catcher, "called a great game today"? Of course not, because he really isn't calling very many pitches. Now, we've all seen the knuckleball catcher struggling to corral these knuckleballs, but in some ways, Mirabelli has it easy: instead of studying video of opposing batters and noting their weaknesses and strengths, he can go out and party all night (or stay home and read spy novels—I do not know where his preferences lie), because the "game plan" is just to throw a flock of knuckleballs down the middle.
In another sense, of course, Mirabelli has it anything but easy. He's got to catch the damn thing, which is not exactly child's play: Joe Torre once said that you don't catch a knuckleball, you defend against it. And Mirabelli has to try to throw out opposing basestealers, who seem to be starting their slide into second while Wakefield's butterflies are still wending their way towards home plate. Unsurprisingly, Wakefield is generally among the American League leaders in stolen bases allowed.
When to throw something else
I throw 90% knuckleballs. The other 10% are prayers. I probably could throw other pitches. The only reason I don't is that I love pitching in the major leagues.
As mentioned above, Wakefield throws a knuckleball about 80% of the time. Of the other pitches, about three-fourths of them are fastballs and one-fourth are curveballs. Now Wakefield's fastball, as we saw above, comes in at around 75 mph, so its effectiveness clearly depends on it not being a knuckleball.
So when does Wakefield decide to change gears and throw something other than the knuckler? The table below shows how often Wake throws a particular kind of pitch depending on the count. So, when the count is 0-0, Wakefield throws the flutter-ball 88% of the time, the fastball 10% and hardly any curves at all.
Pitch Selection for Different Counts +------+-----+------+------+------+ | Cnt | NP | KB% | FB% | CB% | +------+-----+------+------+------+ | 0-0 | 349 | 0.88 | 0.10 | 0.02 | | 0-1 | 156 | 0.92 | 0.02 | 0.06 | | 0-2 | 83 | 0.90 | 0.02 | 0.07 | | 1-0 | 138 | 0.78 | 0.20 | 0.02 | | 1-1 | 123 | 0.91 | 0.06 | 0.03 | | 1-2 | 97 | 0.87 | 0.02 | 0.11 | | 2-0 | 44 | 0.52 | 0.41 | 0.07 | | 2-1 | 55 | 0.62 | 0.36 | 0.02 | | 2-2 | 78 | 0.96 | 0.04 | 0.00 | | 3-0 | 16 | 0.31 | 0.38 | 0.31 | | 3-1 | 21 | 0.48 | 0.52 | 0.00 | | 3-2 | 35 | 0.54 | 0.40 | 0.06 | +------+-----+------+------+------+You can see that as a general trend, Wakefield will throw fewer knuckleballs as he falls behind in the count. When the count is 3-0, for example, Wake throws the knuckler 31% of the time, with the rest being roughly split equally among fastballs and curves.
All Red Sox fans know the sinking feeling when Wakefield gets behind in the count and is forced to throw his 75 mph heater. We start to feel queasy at the prospect, we squirm in our chairs and get ready to turn away in horror when Wake's fastball gets launched into low earth orbit to come crashing down on the Massachusetts Turnpike like meteorites from space. The Boston Police have been known to halt traffic on the Pike when Wake goes to a three-ball count: the populace must be protected.
One way to beat the knuckler
Mark Ellis was having a hard time against Wakefield in a game this season. He had struck out swinging on knuckleballs his first three trips to the plate. As he strolled to the plate for the fourth time against the wily Wakefield, he was formulating Plan B in his mind (this is pure conjecture on my part). Wake's first pitch was a knuckleball (it almost always is, as we have seen) that was just a hair outside. He followed with two straight curveballs (!), both taken by Ellis, to bring the count to 2-1. Wake confounds again by throwing the fastball and Ellis again takes it: strike two.
So, there is some strategy going on here, after all. After making Ellis look foolish with the knuckler in the first three at bats, Wake throws only one knuckleball in the first four pitches. Ellis is hoping for a knuckler at this point, his Plan B depends on it. Wake obliges by throwing the knuckleball at 2-2 (as expected, see table above) and it flutters towards the inside part of the plate. Ellis executes a slight but perceptible rotation of his front shoulder towards the plate.
The butterfly caresses him gently on the left biceps and Ellis trots down to first base—perfect execution of Plan B. The normally unflappable Wakefield has some words with the home plate umpire, but to no avail. Wakefield usually hits quite a few batters, partly because nobody knows where the damn pitch is going, but also because batters are more than happy to take first base in exchange for a slight tingling sensation on their shoulder.
Drilling down to pitches
With a reasonable sample of pitches thrown by Wakefield, we can start to look at what happened on any given thrown pitch. Let's first look at the frequency of balls, strikes and balls put in play.
Pitch Results for Tim Wakefield +-----------+--------+-------+---------+-------+-----------+---------+ | PitchType | NP | Ball% | Called% | Foul% | Swinging% | InPlay% | +-----------+--------+-------+---------+-------+-----------+---------+ | KB | 995 | 0.35 | 0.17 | 0.17 | 0.10 | 0.20 | | non-KB | 200 | 0.30 | 0.30 | 0.09 | 0.05 | 0.25 | +-----------+--------+-------+---------+-------+-----------+---------+ | MLB Ave | 279106 | 0.37 | 0.17 | 0.17 | 0.09 | 0.19 | +-----------+--------+-------+---------+-------+-----------+---------+ Called, Foul, Swinging - types of strikesThe first two rows show Wakefield's pitches, divided into knuckler and non-knuckler categories. To give you some idea of typical values, the last row shows the MLB average for all pitch types. The first interesting thing to note is that the knuckleball, by these measures, looks a lot like an average MLB pitch. I wasn't expecting that at all.
The other curious thing regards the non-knuckleball pitches: twice the rate of called strikes and half the rate of swinging strikes. You'd think batters would unload early and often on a 75 mph fastball, but they are clearly surprised by many of these non-knucklers, letting 30% of them pass over the plate unmolested. On the other hand, when they do swing, they don't miss often.
But what happens once the ball is put into play? Well, we're going to be hampered a bit by low sample size, but let's have a look anyway.
Results for Balls in Play +-----------+-------+-------+-------+-------+-------+ | PitchType | NP | Hit% | HR% | BABIP | OPS | +-----------+-------+-------+-------+-------+-------+ | KB | 197 | 0.315 | 0.025 | 0.297 | 0.822 | | non-KB | 49 | 0.265 | 0.020 | 0.250 | 0.673 | +-----------+-------+-------+-------+-------+-------+ | MLB Ave | 53505 | 0.323 | 0.035 | 0.298 | 0.829 | +-----------+-------+-------+-------+-------+-------+Again, we see the knuckler not very different from the average pitch. I was actually expecting the HR% for knucklers to be higher than average and the opposite for BABIP. I was expecting a lower BABIP number for the knuckleball, since knuckleballers are generally known to give up fewer hits on balls-in-play than conventional pitchers.
However, we are plagued by a small sample size here: the one standard deviation uncertainty in the knuckleball BABIP is .032, i.e. the true value could easily be much lower (or higher) than what we see here. As for the non-knucklers, although Wake had great success with them this year, the sample is so small as to preclude any general conclusions.
If it don't break, then hammer it!
As is evident from the movement plot above, some knucklers have very little "knuckle" to them and they end up near the middle of that plot, i.e. little or no movement.
Now, it's possible that the ball breaks more than once on its way to the plate, but we can't tell that from the Pitch f/x data. All we know is that the ball was headed somewhere when it left Wakefield's hand and it ended up very close to that spot.
Some of these pitches that show little movement may have wiggled left, shimmied right and then fluttered back over the center of the plate, while the batter could only blink in wonder. Others, without a doubt, really do go straight in and get clobbered.
With the Pitch f/x data, though, we can compare the results on balls in play for pitches that broke a lot and for pitches that broke very little. We've already seen that the sample size is getting small, but let's forge bravely onward anyway.
I've divided the knuckleballs into three groups with small, medium and large breaks (see graphic on right) and I've determined the results on balls put into play for each group. This table gives the numbers:
Knuckleball Results for Different Amounts of "Knuckling" +--------+----+-------+-------+-------+-------+ | Break | NP | Hit% | HR% | BABIP | OPS | +--------+----+-------+-------+-------+-------+ | Small | 47 | 0.383 | 0.021 | 0.370 | 0.979 | | Medium | 71 | 0.338 | 0.028 | 0.319 | 0.873 | | Large | 79 | 0.253 | 0.025 | 0.234 | 0.684 | +--------+----+-------+-------+-------+-------+
Gee, BABIP really follows the expectations according to the amount of break, doesn't it? Pitches that broke little had a high BABIP of .370, while pitches with large knuckling movement had BABIP of only .234. This may be fortuitous, though, since the uncertainties on these BABIPs are quite large, due to the small sample size. Still, it is rather suggestive, isn't it?
On the other hand, we don't see the astronomical home run rate that I was expecting on the low-movement knucklers. Folks, these are 65 mph pitches that are presumably coming in straight—I would have expected more than one in 47 balls in play to go out of the park. Perhaps these pitches really are wiggling around on the way to the plate, before ending up where they were originally headed.
I want more data
This looks like a promising area for further research, but we're going to need more data. I'd like to get five times as many knuckleballs to look at, but will Tim Wakefield pitch long enough to reach that goal?I'm pulling for him, no doubt, but I'm also pulling for another guy to stick in the big leagues, a 23-year-old reliever for the White Sox, a guy by the name of Charlie Haeger.
References and Resources
- The Knucklebook by Dave Clark is a fun read, with some physics, instruction, history and interviews. Clark also runs the Knuckleball HQ web site.
- The Diamond Appraised by Craig Wright and Tom House is a classic of sabermetric thinking. Wright devotes a chapter to knuckleballers, and finds that the pitch is likely underused.
- This is getting to be a habit, but I'm going to plug The Neyer/James Guide to Pitchers yet again. Neyer penned the chapter devoted to the history of the knuckleball as well as compiling a list of 70 major league pitchers who threw the pitch.
- A Game of Inches by Peter Morris also contains much information about the early history of the knuckler.
John Walsh dabbles in baseball analysis in his spare time. He welcomes questions and comments via e-mail.
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