"The pitch is marked by its velocity being in the low 90s along with tight late break; hitters often believe they were thrown a fastball until the ball breaks just before it crosses home plate. Right-handed hitters have swung through and missed sliders that nearly hit their back feet."

 

                                                                                                                      -Randy Johnson's slider

Even though the mullet-maned 6'10" giant will now be scaring the pants off of hall of fame hitters in Cooperstown, his impact on the game will surely never be forgotten.  Even into his mid-forties, Johnson would continue to make hitters flail wildly at the aforementioned slider, as Mr. Snappy simply refused to slow down. There is little doubt his slider will go down into baseball history as one of the filthiest pitches ever thrown, and it's retirement leaves a big gaping hole that may not be filled for a long time...

Enter Brandon League.

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via blog.seattletimes.nwsource.com

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Yes ladies and gentlemen, Brandon League.  You might be asking yourself "What could this guy possibly be on, mentioning a relief pitcher in the same breath as the all-time K/9 leader?" and for good reason too.  The other half of the kinda-disappointing-fireballers-named-Brandon trade with a mid 90's sinker and not much else has spent the last 5 years bouncing around every level of baseball, never really putting up a good streak of dominance and becoming the postor boy for inconsistency in the process...

But in 2009 something clicked.  His K/9 shot up, his BB/9 plummeted, and just about the only thing that didn't reflect his new-found performance was his merely-average 4.58 ERA.  Matthew goes into detail as to how this transformation occurred over here, and it appears that a lot of it has to do with the increased usage or invention of (depending on how you look at it) a mid-80's offspeed pitch, which gave hitters fits all year long to the tune of a 2.65 runs/100 value. 

Now, a pitch's success is usually a result of 4 different things:

-Movement
-Location (also includes when it is thrown)
-Velocity
-Deceptiveness

Knowing League, location was clearly not a major factor; he has always had problems with location and he often left this changeup up in the zone, and lets face it, he isn't the brightest pitcher to step on a mound.  He also throws from a side-arm slot and pitches from the left-side of the rubber, which helps to reduce a platoon split, but is not deceptive at all.  That leaves velocity and movement, the two factors that make up a pitcher's "stuff" to blame for the success of League's new pitch.  The pitches with a large amount of both are commonly referred to as "filthy," so, exactly how filthy is this pitch?

via www.mopupduty.com

Apparently, it's so filthy that Pitch F/X has trouble deciding what it actually is.  The pitch system identifies League as a pitcher who throws a changeup, slider, and curveball, all at 85 MPH  But we know that he only throws the changeup  (He did throw a slider, but only 2% of the time, and he stopped using it midway through the season), so what's the deal here?

Lets look at the individual movement of each "pitch."  For those who are not educated on pitch f/x, movement is measured based on where the pitch ended up versus a knuckleball of equal velocity in a vacuum, in other words a pitch unaffected by the vorticies created by the seams of a baseball.  Measurements are in inches and cover both the horizontal and vertical planes. 

For horizontal movement, a negative measurement means that the pitch moved inside to a right handed hitter, and a positive measurement means the pitch moved inside to a left hander.  This is the same for both left and right handed pitchers.  For example, a tailing fastball would have positive horizontal movement if it was thrown by a southpaw, and negative movement if it was thrown by a right hander.

For vertical movement, a positive measurement means that the spin of the pitch caused it to sink slower than if gravity were acting on it alone, and a negative movement means the spin assisted gravity in causing the pitch to sink.

For reference, here are the approximate movement styles for each type of major league pitch.

Rising Fastball: little horizontal tail, lots of rise (10+).
Tailing fastball: >5 inches horizontal tail, rise (8+).
Sinking fastball: >5 inches horizontal tail, little rise (8-).
Cutter: 'Sliding' horizontal movement (opp. of tail), rise.
Slider: Horizontal and Vertical movement around zero, tends to rise and slide.
Curveball: Varying levels of slide and lots of negative rise.
Changeup: Tailing movement, little rise (but almost always positive)

Enough chit-chat, here are the numbers:

Changeup:

-Horizontal: -6.8
-Vertical: -1.3

Curveball:

Horizontal: -5.6
Vertical: -4.8

Slider:

Horizontal: -2.5
Vertical: -3.2

Judging by the horizontal movement, the pitches are definitely changeups.  6 inches of horizontal movement is impossible to achieve with a supinated (slider/curveball/cutter) pitch, and the "slider's" numbers appear to be influenced by the few he actually did throw, and would look more similar to the other two categories if they were omitted. 

What really jumps out at me, however, is the vertical movement on these pitches; I have never seen a changeup with negative vertical movement before, and the closest any other has come that I know of is Max Scherzer's, which rises 1.4 inches!  This hold's especially true for the pitches labeled under "Curveball," which sink almost 5 inches more than a spinless pitch ON AVERAGE!  That's the type of movement you would expect from an actual curveball; it's movement is only slightly less than that of AJ Burnett's.  Given his arm slot and location on the rubber, such a pitch would also appear to drop straight down to a hitter, so a platoon split would not be likely.

via assets.sbnation.com

(Thanks Jeff)

And here's the movement plot for the same outing this GIF was taken from. (August 10)

via www.fangraphs.com

Imagine yourself as a hitter versus Brandon League.  As if a 98 MPH sinker that's hard enough to hit in its own right wasn't enough, you now have to deal with a pitch that looks just like a fastball, starts at your belt and ends up in the dirt by the time the catcher grabs it.  Oh yeah, it's also sits in the mid-80's and he's liable to throw it at any time. Now, suppose you could somehow manage to hit this whiff machine, let alone be able to pick it up and avoid swinging at it (which hitters failed to do 35% of the time last year), tough luck.  League can throw an equally filthy version with less sinking action, freezing you for a called strike or inducing a whiff/weak contact.  All I have to say is, good luck with that.

League had a 6.23 ERA on artificial surfaces last year, most of it in his own building; no doubt as a result of numerous ground balls speeding right out of the infield, and a 2.3 ERA on grass in similar inning samples.  Hitter's OPS'd .834 on turf and .578 on grass as well, ridiculous.  Both splits are bound to regress, but if he pitches anywhere near his 2009 level he is going to absolutely dominate major league hitters, and he can thank most of that on his changeup, which shall now be referred to as THE SOILER OF PANTS, heir to the title of 'filthiest pitch in baseball.'