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  • pFX

    On Gameday, there is a measurement for every pitch called "pFX" measured in inches. Anyone know, for sure, what this means? I have searched and found various answers, none of which satisfy my desire to know.

    Please help a SABRmetric rookie.
    Last edited by jestimator; 05-15-2008, 09:57 AM.

  • #2
    From the Gameday Blog:

    A: "Break" is the greatest distance between the trajectory of the pitch at any point between the release point and the front of home plate, and the straight line path from the release point and the front of home plate. "Pitch-f/x" is the distance between the location of the actual pitch thrown over the plate, and the calculated location of a ball thrown by the pitcher in the same way, with no spin. Or, in more common terms, this is the amount of "movement" the pitcher applies to the pitch. A faster, straighter pitch like a fastball will have a higher Pitch-f/x value than a slower, breaking ball like a curveball, which will have a higher Break value.

    "Can't anybody play this here game?" -- Casey Stengel


    • #3
      I guess the ideal knuckleball should have a PFX of 0?

      No spin and all...


      • #4
        Actually, a knuckleball may *Average* 0, but individually, it's, as we expect, all over the place. Here's a fantastic set of charts:

        Author of THE BOOK -- Playing The Percentages In Baseball


        • #5
          Originally posted by Tango Tiger View Post
          Actually, a knuckleball may *Average* 0, but individually, it's, as we expect, all over the place. Here's a fantastic set of charts:

          Wakefield's "break" graphs crack me up every time I see them. -j
          My blog: On Baseball and the Reds


          • #6
            Wow...Wakefield's KB is different every time he throws it..that's probably why it's catches the wind a little different each time and breaks in a different direction.


            • #7
              pFx = "drop"

              hey, jesti, i'm tink3r from the MLB Fantasy (MLBF) message boards .. i noticed your question and recently tried to answer the same question for another poster at the MLBF game message board .. the result was a late night rambling thread where i tried to put pFx into some meaningful perspective .. i have watched many games on Gameday and pFx has been perhaps the most difficult of the pitching metrics for me to understand

              after a few hundred words and examples, it came to me that "drop" might be the best single word to describe pFx .. checkout my replies at the thread Gameday pFx .. my ramble is far from a definitve answer, but i like the concept of "drop" for pFx .. i'm very curious to see if it makes sense to anyone else with an interest in pFx

              techincally, according to the Gameday description cited above, "'Pitch-f/x' is the distance between the location of the actual pitch thrown over the plate, and the calculated location of a ball thrown by the pitcher in the same way, with no spin." .. for me, i visualize this as "drop" or the difference between the actual pitch location and the theoretical pitch location with "no spin" .. frankly, i'm unsure whether the actual pitch or the theoretical pitch is higher or lower .. it may just vary between pitches based on the type of "spin"

              the Gameday description goes on to say, in the next sentence about pFx, "Or, in more common terms, this is the amount of 'movement' the pitcher applies to the pitch" .. for me, that statement doesn't make sense when applied soley to pFx .. to me, i think of movement as the combination of break and drop on a pitch, BRK and PFX in Gameday terms

              also, i saw Wakefield's last outing on Gameday .. it was fascinating to watch and the pFx was definitively not zero .. while a knuckball is released with no spin, the effects of even the slightest breeze and various other atomospheric conditions, not to mention nicks in the ball, apparently cause the actual pitch to have its characteristic random movement .. i suspect the theroretical pitch with "no spin' is derived from a pure trajectory calculation based on speed and location at the release point - a very simple and fascinating calculation itself

              anyway, i'm a rank newbie here, but have a bad case of baseball fever this year and Gameday's pitching metrics have been one of the most infectious new things i've seen .. so, this seemed like a good place for my first post


              • #8
                12-6 curveballs (which drop) have no PFX.

                The word you're looking for is "run"...when a fastball runs in on a hitter, it has "run"...and a BIG PFX score.


                • #9
                  "run" , eh .. i never have really understood that term .. but when you say "run in" to me that describes horizontal movement, while pFx seems to clearly describe vertical movement .. i could well be over-simplifiying the case too .. i'm trying hard to "see" these pitching metrics in x, y, z co-ordinates

                  so, could you elaborate on "run"

                  also, i'm just a number cruncher, so i have little actual practical knowledge of pitching mechanics .. when i orginally began thinking of "spin" it made sense in the context of a curveball only .. on refection, i assume a fastball may have spin, too - probably backspin .. but again, i'm just guessing not throwing .. any comments there from you or ex-pitchers would be most welcome

                  btw, a 12-6 curveball would have a pFx value, as i understand it .. pFx for curveballs is generally less than pFx for a fastball, but it is not zero .. i don't think i've ever seen a pFx value of 0 .. have you?

                  Last edited by Tink; 06-01-2008, 03:00 PM.


                  • #10
                    I don't know much about the mechanics either...not specifically anyway...I know what each pitch "does" terms of spin...just from observation, but I don't understand the physical processes in great detail.

           not just lateral movement...and break is not just vertical movement.

                    Run is action on a pitch that defies the parabola. A fastball has a parabolic arc just as a curve ball's just very tiny curvature. A running fastball moves in a way that takes it off its' original parabolic arc...both down and sideways.

                    Break defines the depth of the parabola. A big break implies a steeper parabolic arc.


                    • #11
                      i like and can relate to your terminology there, Matt .. but a pitch clearly moves in 3-space .. from a side view, a pitch has a well defined parabolic arc .. from that same side view, i think what we are seeing is merely the arc of the actual pitch .. overlay on that image the theoretical pitch from the same side view .. once again we see an arc, but neither arc relates directly to pFx as i "see" it .. those arcs are simply a relfection of gravity and friction on the ball traveling toward home plate .. my understanding of PFX, from that side view, is the measurment of the difference between the two points where the actual and theoretical pitch cross the plate (front, back, or middle of plate i have no clue) .. that distance is pure vertical movement and what i see as "drop"

                      now, shift to a top view of the same pitch .. there we're going to see an arc too .. somewhere within that arc is the break, or Gameday's BRK value, as i understand it .. i'm not sure exactly how that curve is going to look, but i don't think a curveball is thrown "out" and then comes "in", if so certainly not by very much .. therefore, the release point is probably the starting point when measuring BRK .. as the pitch curves, it seems to me the BRK would be calculated (in this top view) as the distance between the release point (or the outer edge of the arc, if greater) and the point where the pitch crosses the plate .. that is pure lateral movement

                      when you say " not just lateral movement...and break is not just vertical movement", i'm a little confused which is nothing new .. for me, break (BRK) is lateral movement, PFX is vertical movement .. "run" seems to me to be synonomous with "movement" which both describe overall movement of a pitch, both lateral and vertical

                      using these perspectives, the front view of a pitch (an umpires view sketched on flat surface) would most likely resemble a straight line from release point to destination, where the pitch crosses the plate .. it would of course seldom be a straight line, but would be a much more compressed curve than from the top or side view

                      how does all that look to you? i'm sure some one has posted some 3-D images of these pitches somewhere .. i'd sure love to see what they look like - a picture would be well worth a thousand words


                      • #12
                        i just checked out the graphs jinaz recommended at BrooksBaseball above .. i narrowed the set of data to a single inning of the 5/29 CWS vs. TB game Contreras against RHH reducung the data points to only 9 pitches .. the detailed data is also available in a seperate table .. no clear answers there, but certainly worth looking at .. particularly the headings on his graphs .. he alludes to "vertical break" and to "horizontal break" .. there is no indication whether one is BRK or PFX .. as i said, i could easily be over simplifying this whole process vainly in search of x, y, and z co-ordinates

                        one thing that really surprised me is that "spin" is actually claibrated in RPM .. one chart titled Spin Direction x Spin Magnitude is especially interesting there .. i'm still clueless what it all means, but maybe getting closer


                        • #13
                          OK...the reason I came to the conclusions I did:

                          Pitch type and typical BRK and PFX values...

                          Felix Hernandez' 12-6 curve: 10" BRK, 2" PFX
                          Ryan Rowland-Smith's 45 degree curve: 9" BRK, 6" PFX
                          Sean Green's Slider: 7" BRK ,10" PFX
                          Felix Hernandez' 2-seam fastall: 2" BRK, 12" PFX
                          Brandon Morrow's 4-seamer: 2" BRK, 15" PFX
                          Jamie Moyer's Change-up: 5" BRK, 5" PFX

                          If PFX were "drop", then the 12-6 curve would have a big PFX...not a big BRK.
                          If PFX were "drop" then Brandon Morrow would definitely NOT have a big PFX on his 4-seamer...that thing has devastating late movement up and's explosive...but it doesn't runs.


                          • #14
                            Hi guys. Someone from these boards sent me an email, and I figured I would answer the question in the thread.

                            The easiest way to do so is to quote Alan Nathan, who has an extensive guide to using PitchFX data:

                            pfx_x,pfx_z: The deviation (in inches) of the pitch trajectory from a straight-line in the x (horizontal) and z (vertical) directions between y=40 ft and the front edge of home plate, y=1.417 ft. It is important to note two things. First, the initial value is y=40 ft, regardless of the value of the initial value y0 (defined below). If the pitcher's release point had been used (approximately y=55 ft), then the deviation would have been nearly twice as large. Second, the effect of gravity has been removed from pfx_z, so that both parameters are the "break" of the pitch due to the Magnus force on a spinning baseball. Note that the online Gameday reports the quantity pfx, which is presumably the square root of pfx_x^2+pfx_z^2. Given our sign conventions, a positive value of pfx_x cooresponds a deviation to the catcher's right and a negative value to the catcher's left. Similarly, a postive value of of pfx_z is a pitch the drops less than it would from gravity alone (most pitches fall in this category), whereas a negative value is a pitch that drops more than from gravity alone (e.g., a "12-6" curveball).

                            So, actually, PFX measures both horizontal and vertical drop, but then MLB does some strange stuff to it instead of reporting the actual values.

                            It is probably easiest to look at this in terms of graphs:

                            On the X axis here is Pfx_x, and on the y axis here is Pfx_z, the parameters that correspond to the movement in both the x and y axis on a graph if you were a hitter.

                            From this, we can see that Bartolo Colon is throwing essentially 4 pitches - a 2 seam fastball that breaks about 8in inside and 4in "up" to RHH and a 4seam fastball that breaks about 5in inside and about 11in "up" to RHH (note, pitches don't actually break up because the effect of gravity has been removed from the pitches here, they just fall slower than normally due to spin); he also throws a changeup (rarely) that breaks somewhat erratically and a slider that sweeps across the plate, averaging about a 3in outside break (but, consider that this breaks about a foot more to the right than his fastball does, and is thrown considerably slower).

                            I would refrain from using the PitchFX variables as reported by gameday on the MLB applet, because those are further transformed. Instead, it is better to use either the actual data or these graphs which show actual variables.



                            • #15
                              Spin is calculated from the formula here:

                              In fact, that whole Wiki Page might be some help.



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