PFX vs. BRK and Pitch Types

It’s been a while since we posted a glossary or Q&A explaining some of the features of Gameday, so here’s a link to the one we did last spring.

Also, here are answers to two commonly asked questions about Gameday:

Q: What are the PFX and BRK values?

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.

Q: How do you determine pitch types?

A: We compare specific properties of each pitch — its speed at release and where it crosses the plate, velocity and acceleration in three dimensions, as well as angle and degree of break — to those of previously defined “control” pitches, then evaluates the similarity of each property to that of each control pitch to determine an overall likelihood of the pitch type. The most likely pitch type is then selected.

Additional logic is applied to weight the results towards specific pitch types for each pitcher; for instance, this will limit the likelihood of a pitch being labeled as a split-finger fastball if the pitcher is not known to throw this pitch. However, certain pitch types are not completely restricted, in the event the pitcher later introduces that pitch to his repertoire.

* * *

Thanks for everyone’s feedback, we really do read everything even if we don’t respond that often. We hope everyone enjoys the features we have added and changes we’ve made, many of which were in direct response to comments on this blog. Plus, we have some additional cool new stuff that we hope to release within the next few weeks.

Happy baseball!




    That’s nice, but I just want to remind you that the new Gameday (still) doesn’t work at all on Linux.


    thanks, but understanding BRK, PFX, and the other pitch metrics is still somewhat confusing .. you say, “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.” .. that sentence, on first glance made no sense to me .. so, i looked at a selection of pitches thrown by the same pitcher to one batter – 4 curveballs, 3 fastballs – with these metrics (a little hard to read below without linefeeds, so i included slashes)

    SPD BRK PFX //

    Fastballs //
    91 7″ 14″ //
    92 7″ 12″ //
    92 8″ 13″ //

    Curveballs //
    77 11″ 6″ //
    78 13″ 7″ //
    77 13″ 7″ //
    78 12″ 8″ //

    .. BRK and PFX behave as you said .. now the sentence makes more sense .. when i consider “movement”, common sense tells me that a curveball has more “movement” than a fastball .. this is seen in the metrics by the 11-13″ BRK of the curveballs compared to the 7-8″ BRK of the fastballs thrown in these selected pitches .. that makes sense, as well

    .. but now i look back at PFX ranging from 12-14″ for a fastball and 6-8″ for a curveball .. this seems counter-intuitive .. if PFX measures “the distance between the location of the actual pitch thrown over the plate, and the calculated location of a ball thrown … in the same way, with no spin”, it seems to me a curveball with more “spin” than a fastball would have a greater not lesser PFX value .. yet a curveball has a lower PFX than a fastball .. thus, i’m right back to my original point of confusion with PFX

    .. clearly the values from the selected pitches confirms and supports your statements, i’m just still having a hard time “seeing” the reason why .. for me, PFX, the difference of an actual pitch and the same pitch with “no spin”, implies the comparison of two trajectories .. why this difference is greater for a fastball than a curveball still eludes me .. but then i never could “see” a curveball .. regardless, i’m really enjoying trying to better understand these metrics

  3. Gameday

    Hi ebx327, the answer is actually very straightforward and has to do with velocity and gravity. Without overstating (or mis-stating) the physics involved, a fastball is thrown with greater backspin and at higher velocity, so it will resist gravity and therefore not sink as far as a no-spin pitch would. Therefore it has a relatively low BRK value (because it doesn’t curve much compared to a curveball or slider) but a higher PFX value, because a no-spin pitch will drop more than a fastball.

    A curveball is thrown with more top spin and at a lower velocity than the fastball, so it actually drops at a faster rate than the fastball and therefore has a lower PFX value because gravity influences it more than the fastball.

    That’s the simple answer, hope it helps!
    Gameday folks

  4. mihalik33

    This has nothing to do with the PFX and BRK, but I’m not sure if the comments on the earlier topics are still being addressed.

    I cannot get Gameday to work. I have been trying to use Gameday since the beginning of the season, and I was hoping that this bug was just part of the initial Gameday release and would soon be fixed… Every time I’ve tried to use it this season, I get the same blank, gray applet with this message:

    “This content requires Adobe Flash Player 9. Would you like to install it now?”

    I’m using Windows XP, Firefox, and Flash (all current versions). I’ve paged through all of the comments on this blog regarding Flash, read the Known Issues, and I’ve un-installed and re-installed Flash as recommended. None of this has affected Gameday, and it still tells me that I’m not using an up-to-date Flash Player (even though I clearly am).

    I’m fairly sure that I’m not the only one experiencing this problem, but is there any known fix for this? I don’t get this message for any other websites or Flash content around the web… it’s just Gameday. If it’s an error on Adobe’s end, could you at least point me in the right direction on what is causing it and how I could fix it?

    Please let me know. Thanks.


    To Gameday Folks, RE: ebx327

    I was really disappointed to read your response to the question posted by ebx327 on May 17th. Unfortunately your description of the physics of baseball pitches is too simplistic and flawed. The trajectory of a baseball thrown from a pitcher’s hand has nothing to do with the differential force of gravity (which is EXACTLY the same regardless of the pitch type or speed) but has everything to do with air friction and drag. It is the position of the stitches with respect to the trajectory of the thrown ball which makes for a fastball, curveball, slider, knuckle ball, or any other type of breaking ball. It is the combination of drag forces which make a ball break, drop, or “rise”, and not the “simple” combination of velocity and gravity. Without the effects of air resistance a four-seam fastball thrown at 97mph (directly parallel to the ground) would hit the ground at the same time as a ball simply dropped out of a pitchers hand. This is because the acceleration of gravity is the same regardless of velocity.

    To ebx327, I know this explanation probably doesn’t help much but there are a couple of good books out there on the physics of baseball and a few websites which aren?t too shabby as well. If you don?t hear back with a better explanation from Gameday and you?re still interested I strongly suggest checking some of them out. Personally I like the fact that the problem isn’t so easily answered; it adds even more mystique and beauty to the game. Good question!!

    And to Gameday, I suggest you check your facts next time before responding too hastily to questions.



    The Gameday folks were correct about the physics involved, although it appears you didn’t understand what they were getting at.

    There are three main forces acting on a spinning baseball: gravity, drag, and the spin force (also called the Magnus or lift force).

    The drag force mainly acts to slow a pitch down, it doesn’t have much effect on the movement/break of a pitch, except for very, very slowly spinning pitches (i.e., knuckleballs).

    The force of gravity is the same on all pitches, but it has a greater effect on the movement of slow pitches because it has longer to act on them before they reach the plate. Curveballs and changeups drop more due to gravity than fastballs do because they are slower pitches.

    Finally, the spin force acts differently on fastballs and curveballs, as the Gameday folks described. Because a fastball is thrown with backspin, the spin force pushes the ball up, counteracting to some extent the force of gravity that is pulling the ball down. This makes the fastball trajectory straighter. Because a curveball is thrown with topspin, the spin force pushes the ball down, reinforcing gravity which is also pushing it down. This makes the curveball drop even more.

    Thus, the curveball trajectory has a big bend and the fastball trajectory is relatively straight. The amount of bend in the trajectory is what is being measured by the BRK parameter on Gameday.

    The amount of deflection by the spin force is what is being measured by the PFX parameter on Gameday. This PFX deflection is mostly upward for a fastball, meaning that it counteracts roughly 10 or so inches of the drop due to gravity, and the PFX deflection is mostly downward for a curveball, meaning that it adds an additional 6 or so inches of drop in addition to that from gravity.


    I think it’d be great if there were a little more information displayed on the pitcher’s tag on the left side of the screen, over the current batter and on deck/in the hole batters. Currently, it just displays three lines — name/number/handedness, record and ERA, and pitch count with strikes and balls. It’d be much more useful if it would also display a fourth line with the pitcher’s current line, much like the batter’s tag displays their stats for this game (third line: X-for-Y; fourth line: flyout, strikeout, etc.). Even just a count of runs, hits, strikeouts and walks charged to that pitcher would be awesome, if not a true linescore.


    I have never been abe to get the strike zone shading to show in gameday with Firefox or IE. Does anyone know why that might be?

  9. cubbies011

    Is there anyway that you could implement “hot zones” (hit zones) for all the batters? Also, it would be nice if there was a option to see a spray chart of the different teams and where they are hitting the ball in the stadium. And maybe you could add more stats to the players and pitchers when you click on their names, like add the stats of pitcher vs. batter. If you could add all of this, I believe gameday would be better than ever.


    3D is ok, but video isn’t working (at least on Giants v. A’s), and the pitcher/batter matchups on the left side have been stuck for about 3 innings.

  11. cjt782

    hopefully the gameday designers see this…

    i noticed a problem with Tim Wakefield pitching:
    according to gameday, Wake doesnt throw any pitch accept a knuckle. the problem is of course that his fastball is about 70 mph.
    generally if the speed is over 70 and the break is under 10″ its actually a fastball, but gameday reports a knuckle everytime.
    example: 4th inning second batter is longoria
    first pitch listed at 72 mph, 7″ BRK and 14″ PFX
    wake does NOT throw a knuckle that hard

    i’m not sure what can be done about this, but i’m guessing that it applies to other situations as well (for example Seattle knuckleballer R.A. Dickey probably)

  12. papasamone

    I see that Joe Giraldi is taking us to a new championship, the one of loosers. What has happened to our hard hitting team? These are not the Yankees that we are so happy to watch playing. I know that one person doesn’t make a team, but if the leader of the team can’t function right and make the right decisions, and take a correct direction, then the team is lost. I honestly believe, (and many others have told me the same thing), that he was the wrong choice to lead the Yankees. The amount of losses have proved it.
    I have been a Yankee fan for 54 years and it hurts to see my team in this situation.

  13. papasamone

    The Yankees are getting ready for another championship. However, if Joe Giraldi doens’t know how to do his job, they won’t make it. Giraldi didn’t take the team to last year’s victory. The team did that. There is no “I” in team. Matsui, Damon, Cabrera,Giambi were all thrown out but look how good they still are. Now Giraldi has players that are useless and he keeps them. They don’t produce, get rid of them. AJ Burnett has been losing so many games and is playing like he doesn’t want to be there and Giraldi won’t bench him or send him to minor leagues. The new outfielders, short stop and other new players are useless. I can’t believe they were swept by the Orioles and lost two to the Rangers and two to the Rays. Giraldi lets his pitchers continue getting hammered even after they mess up. I see other managers change pitchers when the other team scores one or two runs on them.


    nice work, I’ve never seen the term “break” so eloquently described! I didn’t know there was a calculable formula to it, but I guess that makes sense. I’m taking my vacation bible school to a Reds game this weekend, and I’ll be sure they all do their math homework first! : )

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