Transcript Physics 199BB The Physics of Baseball

What Have We Learned from the
PITCHf/x System?
A report from the summit
Alan M. Nathan, with help from John Walsh,
Mike Fast, Josh Kalk, Dan Brooks, and the
good folks at Sportvison, mainly Marv White.
• What is PITCHf/x and how does it work?
• What are we learning from it?
• Outlook for future
webusers.npl.uiuc.edu/~a-nathan/pob/pitchtracker.html
sportvision.com/events/pfx.html
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PITCHf/x is a pitch-tracking system installed in
every MLB venue—a joint venture of
Sportvision & MLBAM
ESPN K-Zone
MLB Gameday
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Fox Trak
How Does PITCHf/x Work?
• Two video cameras track baseball in 1/60-sec
intervals
– usually “high home” and “high first”
• Software to identify and track pitch frame-byframe in real time  full trajectory

lots of other stuff
Image, courtesy of Sportvision
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What kind of “stuff”?
• Pitch speed to ~0.5 mph
– at release and at home plate (they are different!)
• Pitch location to ~0.5 inches
– at release and at home plate
• “movement” to ~2.0 inches
– both magnitude and direction
• Initial velocity direction
• Type of pitch
– more on this later
• And all of this can be correlated with what the batter
does!
– a complete digital record exists!
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And the good news is….
…all these data are freely available online! For info on
how to download, establish data base, etc., see …
– mvn.com/mlb-stats/2008/01/14/a-pitchfx-primer/
Mike Fast
– http://brooksbaseball.net/pfx/
Dan Brooks
– http://blog.stealingfirst.com/2008/03/07/how-to-link-pitchfxto-retrosheet/
Dan Turkenkopf
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What can we potentially learn from
these data?
• Things of interest to physicists
– Effect of air drag and spin
– The mysteries of the knuckleball
• Things of interest to players, scouts, fans
– What do pitchers thrown and when do they throw it?
– What are their most/least effective pitches?
– What makes an effective fastball, curveball, slider, …?
• speed, break, location, …
– How do hitters perform against different pitch types, locations,
speeds, etc.?
– What is effect of pitch sequencing?
– Other questions limited only by one’s imagination
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Example:
Pitch Sequence Leading to Bonds 756th Home Run
An obvious mistake:
Catcher was set up low
and away
4.0
1
3.5
7
3.0
2.5
4
3
2.0
6
1.5
5
1.0
2
0.5
0.0
-3
-2
-1
0
px
1
2
3
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Example 1: Pitch Speed--PITCHf/x vs. the gun
• Pitched ball loses about 10% of speed
between pitcher and batter
• Average speed <v> is ~95% of release
speed
y = m1 * M0
90
85
m1
Chisq
R
Value
0.89296
56.865
0.98879
75
80
Error
0.00086858
NA
NA
PITCHf/x is almost surely
more accurate than the
gun
80
75
70
65
60
70
85
v (mph)
0
90
95
100
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Example 2: Pitching at High Altitude:
Higher <v>, less movement in Denver vs. Toronto
7.5%
10%
loss of velocity
total movement
12”
8”
PITCHf/x data contain a wealth of information about drag and lift!
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Using PITCHf/x to Classify Pitches
Most techniques based on …
– Speed
– Horizontal and vertical movement due to spin (“pfx”)
• Same as deviation from straight line, with gravity removed
– Examples:
• FB w/backspin  upward movement
• CB w/topspin (12-6)  downward movement
• Sidespin  sideways movement
pfx,z
pfx
pfx,x
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Pitch Classification: LHP Jon Lester, Aug. 3, 2007
4-seam fastball
2-seam fastball
cutter/slider
curveball
>90 mph
80-90 mph
<80 mph
Wikipedia: Lester, a left-hander, pitches from a low
three-quarters arm angle with a deceptive delivery. He
features 4-seam fastball (89-95), a cut fastball (86-89),
a slider (75-80), a plus-changeup, and a good curveball
(72-78 mph).
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By comparison, look at Brandon Webb
Brandon Webb
Plots, courtesy of Dan Brooks
Comparing FB upward movement:
• Lester ~ 11”
• Webb ~ 3”
Jon Lester
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PITCHf/x tackles the knuckleball – John Walsh
http://www.hardballtimes.com
•
•
•
fastball
Classify pitches using
vertical and horizontal
break plus speed
Compare “normal”
pitcher (C.C. Sabathia)
with k-baller (Tim
Wakefield)
“Randomness” of k-ball
break is evident in
PITCHf/x data
slider
knuckler
change
curve
http://www.hardballtimes.com/main/article/butterflies-are-not-bullets/
•
•
Example analysis: What
happens when knuckleball
does not “knuckle”?
Split k-balls into 3 groups
– small, medium, large
break
Amount
of
Break
Pitches
put in
play
OPS
against
Small
47
.979
Medium
71
.873
Large
79
.684
(small sample size, though)
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What makes an effective slider?—C. C. Sabathia
Josh Kalk, THT, 5/22/08
C. C. Sabathia: FB vs. Slider
7
6
5
95 mph fastball
This slider is very
effective since it looks
like a fastball for over half
the trajectory, then seems
to drop at the last minute
(“late break”).
~4 inches
4
3
82 mph slider
2
1
~12 inches
0
0
10
20
30
40
50
Distance from home plate (ft)
14
0-0 Count,
Normal SwingZone Width
Batter Selectivity
Strikes
0
1
Protecting the Plate
When Down 0-2
2
0
Balls
1
2
Hitters are
more
selective
when ahead
in the count
3
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Analysis by Dan Brooks, brooksbaseball.net
Scouting Players with PITCHf/x: Roy Oswalt 2008
Mike Fast
What do his pitches look like to the batter?
What is his pitch selection?
4-seam
Fastball
2-seam
Fastball
Curve
Slider
Change
LHH
32%
29%
23%
8%
8%
RHH
34%
28%
15%
23%
0%
Total
421
363
234
204
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How does he locate his pitches and
what results does he get?
What are his most effective pitches?
Run value/pitch
Slider
-0.023
Two-seamer
+0.007
Four-seamer
+0.013
Changeup
+0.021
Curveball
+0.039
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How Fast Should a Fastball Be? – John Walsh
http://www.hardballtimes.com
high and tight
low and away
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From PITCHf/x to HITf/x:
Tracking Batted Balls
• What can be measured with existing
cameras?
– Speed of ball off bat
• the ultimate metric of good hitting
– Horizontal and vertical angle
• Together, these highly constrain full
trajectory—where does the ball land?
– use to evaluate hitting
– use to evaluate fielding
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A computational example:
• V0=90 mph, 0=350
– measured by PFX cameras
•  = 1462-2284 rpm
– not measured by PFX cameras
• A model for drag and lift
100
80
60
2284 rpm, R=335 ft
1827 rpm, R=331 ft
1462 rpm, R=327 ft
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• landing points
differ by ± 4 ft
• a promising
technique
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0
0
50
100
150
200
x (ft)
250
300
350
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Summary
• PITCHf/x data have the potential to
revolutionize the analysis of baseball
• Some excellent and creative analyses
have already been done
– Expect more as time goes on
• Lobby hard for HITf/x, which adds another
dimension to the revolution
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