Going Deep: Using Pitch Acceleration to Predict Batted Ball Quality

(Photo by Scott Winters/Icon Sportswire)

In the depths of Statcast are a handful of statistics that are tracked, but not displayed prominently. A few such are pitch acceleration metrics, measured at the point of release in three directions. These statistics measure how a pitch should move in the air due to the forces of drag, Magnus effect, and gravity.

A pitch with high acceleration in air intuitively should be harder to hit than one that is flat. To calculate the sum of acceleration of a pitch in three dimensions, it can be represented as the magnitude of a 3D vector (√ax² + ay² + az²). As results tend to cluster around the same baselines for average acceleration on each pitch type, scores for each pitch are represented by its percentile among other pitches of the same type. Pitchers are given an overall score of the average percentile of each pitch they throw.

Firstly, it is important to establish that acceleration percentiles (ACC%) are repeatable year to year to show that pitchers have influence over the effects of acceleration in air.  The samples used were pitchers who threw at least 50 innings between 2016-17 (227 pitchers) and 2017-18 (120), as Statcast data past 2015 is more reliable.

Year	r2 of ACC% with itself year+1
2016	0.516
2017	0.791

In the same sample, these correlations compare similarly to groundball rate allowed and better than strikeout and walk rates, all three well established repeatable skills. The 2017-18 r² was likely higher because almost all pitchers to throw at least 50 innings in 2017 and 2018 so far were starting pitchers who had higher innings totals to stabilize. ACC% also shows some predictive value in pitcher performance on batted balls:

Statistic	2016 r2 with wOBA allowed on batted balls year+1	2017 r2 with wOBA allowed on batted balls year+1
ACC%	0.0264	0.028
GB%	0.0187	0.025
HR%	0.0176	0.01

In both time frames, ACC% performed slightly better than GB% in predicting pitcher wOBA on batted balls. Pitchers with high acceleration percentiles tended to allow weaker contact. While still not the strongest correlation, batted ball results are the most confounding element of pitching to project. ACC% should be used in conjunction with GB% in understanding how a pitcher may have the ability to suppress contact.

I tested other relationships between ACC% and several statistics such as K% and BABIP and found some other modest correlations, but the most unique value compared to existing statistics came in evaluating batted ball profiles. Another possible application could be noting that a sharp drop in ACC% may indicate a pitcher is injured or has a mechanical issue.

The following are the 2018 leaders among qualified SP and RP. Of course there are some good pitchers who succeed with low acceleration and some mediocre pitchers who remain middling despite high acceleration. ACC% still provides a unique insight to pitcher ability that appears to be at least equal to and possibly more than the value that GB% provides.

Chris Sale’s score of 0.96 means that his average pitch is in the 96th percentile of acceleration adjusted for type. While 0.5 is average, starting pitchers tend to score slightly lower than relief pitchers.

SP Leaders

Rank	Player	ACC%
1	Chris Sale	0.96
2	Charlie Morton	0.90
3	Luis Castillo	0.84
4	Clayton Richard	0.83
5	Sean Manaea	0.81
6	Aaron Nola	0.78
7	Luis Severino	0.75
8	Trevor Bauer	0.74
9	Gerrit Cole	0.73
10	Ivan Nova	0.72
11	James Paxton	0.71
12	Max Scherzer	0.70
13	Justin Verlander	0.69
14	Nick Pivetta	0.67
15	Lance McCullers	0.64
16	Eduardo Rodriguez	0.64
17	Mike Leake	0.62
18	Jose Urena	0.62
19	Carlos Carrasco	0.62
20	Mike Foltynewicz	0.62
21	Kevin Gausman	0.59
22	Tyler Mahle	0.58
23	Jakob Junis	0.56
24	Michael Fulmer	0.56
25	David Price	0.56
26	Reynaldo Lopez	0.55
27	Mike Clevinger	0.55
28	Steven Matz	0.55
29	Jose Berrios	0.55
30	Jake Arrieta	0.55
31	Zack Wheeler	0.55
32	Miles Mikolas	0.53
33	Jacob deGrom	0.53
34	Jhoulys Chacin	0.53
35	Luke Weaver	0.53
36	Gio Gonzalez	0.52
37	Corey Kluber	0.52
38	Zack Godley	0.50
39	Jameson Taillon	0.49
40	Cole Hamels	0.48
41	Bartolo Colon	0.48
42	Vince Velasquez	0.47
43	Blake Snell	0.47
44	James Shields	0.47
45	Julio Teheran	0.45
46	Felix Hernandez	0.45
47	Rick Porcello	0.45
48	Daniel Mengden	0.45
49	Tyson Ross	0.44
50	Patrick Corbin	0.44
51	German Marquez	0.43
52	Lucas Giolito	0.43
53	Sal Romano	0.43
54	Junior Guerra	0.42
55	Dylan Bundy	0.42
56	Marco Gonzales	0.42
57	Dallas Keuchel	0.41
58	Tyler Skaggs	0.41
59	Kyle Freeland	0.40
60	Chase Anderson	0.40
61	Jason Hammel	0.40
62	Sean Newcomb	0.39
63	Kyle Gibson	0.39
64	J.A. Happ	0.38
65	Danny Duffy	0.38
66	CC Sabathia	0.38
67	Jon Gray	0.37
68	Ian Kennedy	0.37
69	Trevor Williams	0.33
70	Jon Lester	0.33
71	Andrew Cashner	0.32
72	Chad Bettis	0.31
73	Mike Fiers	0.30
74	Tanner Roark	0.30
75	Chris Stratton	0.29
76	Jose Quintana	0.28
77	Zack Greinke	0.27
78	Jake Odorizzi	0.27
79	Mike Minor	0.25
80	Andrew Heaney	0.25
81	Alex Wood	0.23
82	Matthew Boyd	0.23
83	Tyler Anderson	0.14
84	Marco Estrada	0.09
85	Kyle Hendricks	0.08

RP Leaders

Rank	Player	ACC%
1	Aaron Loup	0.91
2	Brad Hand	0.90
3	Jared Hughes	0.87
4	Joe Kelly	0.86
5	T.J. McFarland	0.86
6	Brandon Morrow	0.85
7	Jordan Hicks	0.85
8	Blake Treinen	0.85
9	Trevor Hildenberger	0.84
10	Brad Ziegler	0.83
11	Tayron Guerrero	0.83
12	Alex Claudio	0.83
13	Buck Farmer	0.82
14	Felipe Vazquez	0.82
15	Hector Rondon	0.82
16	Matt Barnes	0.81
17	Hector Neris	0.80
18	Joe Jimenez	0.79
19	Chaz Roe	0.79
20	Adam Cimber	0.78
21	Aroldis Chapman	0.78
22	Mychal Givens	0.77
23	Taylor Williams	0.77
24	Miguel Castro	0.77
25	Arodys Vizcaino	0.77
26	Justin Anderson	0.76
27	Craig Kimbrel	0.76
28	Steve Cishek	0.76
29	Kirby Yates	0.76
30	Adam Ottavino	0.76
31	Zach McAllister	0.75
32	Richard Rodriguez	0.75
33	Ryan Tepera	0.75
34	Lou Trivino	0.75
35	Seranthony Dominguez	0.75
36	Jacob Barnes	0.75
37	Jeurys Familia	0.74
38	Chris Devenski	0.74
39	Raisel Iglesias	0.74
40	Sam Dyson	0.73
41	Ken Giles	0.73
42	Collin McHugh	0.72
43	Austin Brice	0.72
44	Jorge De La Rosa	0.71
45	Ryan Madson	0.71
46	Danny Barnes	0.71
47	Will Harris	0.71
48	Jake Diekman	0.70
49	Hansel Robles	0.69
50	Scott Alexander	0.69
51	Amir Garrett	0.69
52	Bruce Rondon	0.69
53	Edwin Diaz	0.68
54	Steven Brault	0.68
55	Jace Fry	0.68
56	Mike Mayers	0.67
57	Kelvin Herrera	0.67
58	Jeremy Jeffress	0.67
59	Bryan Shaw	0.66
60	Paul Sewald	0.66
61	Edubray Ramos	0.66
62	Hunter Strickland	0.66
63	Matt Albers	0.66
64	Kyle Crick	0.66
65	Seth Lugo	0.66
66	Alex Colome	0.66
67	Cory Gearrin	0.64
68	Shane Greene	0.64
69	Robert Gsellman	0.64
70	Edgar Santana	0.64
71	Dan Otero	0.64
72	Zach Duke	0.63
73	Kevin McCarthy	0.63
74	Tyler Glasnow	0.62
75	Dan Jennings	0.62
76	Wandy Peralta	0.62
77	Warwick Saupold	0.62
78	Taylor Rogers	0.62
79	Brad Peacock	0.62
80	Brad Brach	0.61
81	Jesse Biddle	0.60
82	Tony Watson	0.60
83	Dylan Floro	0.60
84	Cam Bedrosian	0.60
85	Matt Andriese	0.59
86	Sam Tuivailala	0.59
87	Archie Bradley	0.59
88	Pierce Johnson	0.59
89	John Brebbia	0.58
90	Bud Norris	0.58
91	Ryan Pressly	0.58
92	Dellin Betances	0.58
93	Shane Carle	0.57
94	Jose Alvarado	0.57
95	Drew Steckenrider	0.56
96	Richard Bleier	0.56
97	David Robertson	0.55
98	Andrew Chafin	0.55
99	Kyle Barraclough	0.55
100	A.J. Minter	0.55
101	Chad Green	0.54
102	Tommy Hunter	0.54
103	John Axford	0.54
104	Santiago Casilla	0.54
105	Jake McGee	0.53
106	Chris Beck	0.53
107	Chasen Shreve	0.52
108	Reyes Moronta	0.52
109	Cody Allen	0.52
110	Jesse Chavez	0.51
111	Matt Magill	0.51
112	Heath Hembree	0.51
113	Josh Hader	0.51
114	Mike Wright	0.51
115	Pedro Strop	0.49
116	Craig Stammen	0.48
117	Chasen Bradford	0.48
118	Matt Grace	0.48
119	Burch Smith	0.48
120	Daniel Hudson	0.47
121	Chris Volstad	0.46
122	Sergio Romo	0.46
123	Hector Velazquez	0.46
124	Ryan Yarbrough	0.46
125	Chris Rusin	0.45
126	Austin Pruitt	0.45
127	Brandon Kintzler	0.45
128	Jonathan Holder	0.45
129	Jim Johnson	0.44
130	Seung Hwan Oh	0.44
131	Pedro Araujo	0.44
132	Josh Fields	0.43
133	Jose Leclerc	0.43
134	Yoshihisa Hirano	0.43
135	Jose Alvarez	0.43
136	Juan Nicasio	0.43
137	Blake Parker	0.42
138	Noe Ramirez	0.40
139	Fernando Rodney	0.40
140	Keone Kela	0.39
141	James Pazos	0.39
142	Joakim Soria	0.39
143	Brian Flynn	0.37
144	Sammy Solis	0.37
145	Erik Goeddel	0.36
146	Emilio Pagan	0.36
147	Justin Wilson	0.36
148	Dan Winkler	0.36
149	Brian Johnson	0.35
150	Wade Davis	0.34
151	Michael Feliz	0.34
152	Sam Freeman	0.34
153	Brad Boxberger	0.32
154	Victor Arano	0.31
155	David Hernandez	0.30
156	Robbie Erlin	0.30
157	Chris Hatcher	0.29
158	Michael Lorenzen	0.28
159	Kenley Jansen	0.26
160	Addison Reed	0.25
161	Pedro Baez	0.25
162	Tyler Clippard	0.23
163	Sean Doolittle	0.20
164	Alex Wilson	0.17
165	Hector Santiago	0.16
166	Fernando Salas	0.14
167	Yusmeiro Petit	0.06