(This was originally published at Beyond the Box Score in 2006)
Most fans know that Gibson had an incredibly low ERA of 1.12
in 1968. Even considering that the league ERA was just 2.98 that year, what he
did is still great. What explains this performance? Did Gibson have a great “stuff”
year? Was he lucky? Or was it a combination of luck and skill? If so, how much
of each?
Luck is sometimes a factor in baseball. Some years a guy
hits well with runners in scoring position (RISP), some years he doesn’t. In
2004, A.J. Pierzynski, for example, hit .272 overall but .307 with RISP. In
2005, he hit .257 overall but only .236 with RISP. Its not likely he forgot how
to hit with RISP all of the sudden. For pitchers, the batting average they
allow on balls in play may be out of their hands (as pointed out by Voros
McCracken). A pitcher might get lucky on balls in play one year, with more
getting caught than normal (or his fielders might be especially good one year).
Is this what happened to Gibson?
To test this, I ran a regression in which a pitcher’s ERA
was the dependent variable and his strikeouts, walks and HRs allowed per 9 IP
were the independent variables. I used the regression equation to predict each
pitcher’s ERA then found out how much it differed from his actual ERA. If a
pitcher had an ERA lower than what his strikeouts, walks and HRs allowed per 9
IP predicted, he most likely gave up fewer hits on balls in play than average.
Here is the regression equation
(1) ERA = 2.19 + 1.436*HR  .159*SO + .303*BB
Again, all stats are per 9 IP. BB includes both walks and
HBP. The data includes all pitchers who qualified for the ERA title from
196368 (I used this period since it was an especially low scoring period).
There were 420 pitchers. The rsquared was .548, meaning that 54.8% of the variation
in ERA across pitchers is explained by the equation. The standard error is
.469.
Plugging Gibson’s 1968 data into equation (1) leaves an ERA
of 2.02. That is a very large 0.90 above his actual ERA of 1.12. So it appears
that he must have done especially well on balls in play (more on this later).
The table below shows the leaders in how much lower their predicted ERA was
than actual their ERA.
Rank

Pitcher

YEAR

ERA

Pred

Diff

1

Rickey
Clark

1967

2.59

3.81

1.22

2

Joe
Horlen

1968

2.37

3.48

1.11

3

Carl
Willey

1963

3.10

4.18

1.08

4

Lee
Stange

1963

2.62

3.68

1.06

5

Jim
Perry

1965

2.63

3.64

1.01

6

Dave
McNally

1968

1.95

2.92

0.97

7

Tommy
John

1968

1.98

2.91

0.93

8

Bob
Gibson

1968

1.12

2.02

0.90

9

Bob
Veale

1968

2.06

2.95

0.89

10

Joe
Horlen

1967

2.06

2.93

0.87

11

Vern
Law

1965

2.16

3.01

0.85

12

Sonny
Siebert

1967

2.38

3.21

0.83

13

Pete
Richert

1965

2.60

3.41

0.81

14

Joe
Horlen

1964

1.88

2.69

0.81

15

Phil
Niekro

1967

1.87

2.68

0.81

16

Tracy
Stallard

1965

3.39

4.19

0.80

17

Bobby
Bolin

1966

2.89

3.69

0.80

18

Denny
McLain

1968

1.96

2.75

0.79

19

Eddie
Fisher

1965

2.40

3.17

0.77

20

Jim
Perry

1966

2.54

3.29

0.75

21

Luis
Tiant

1968

1.60

2.34

0.74

22

Jim
Bouton

1963

2.53

3.26

0.73

23

Jerry
Koosman

1968

2.08

2.80

0.72

24

Milt
Pappas

1965

2.61

3.33

0.72

25

Steve
Blass

1968

2.13

2.85

0.72

Gibson is not first in “Diff” but he did have a big one at
#8 (something intersting is may be going on with the White Sox, with John,
Horlen and Fisher all being up there). The table below shows the 25 lowest
predicted ERAs.
Rank

Pitcher

YEAR

ERA

Pred

1

Bob
Gibson

1968

1.12

2.02

2

Sandy
Koufax

1963

1.88

2.06

3

Sandy
Koufax

1964

1.74

2.16

4

Sandy
Koufax

1965

2.04

2.18

5

Sandy
Koufax

1966

1.73

2.20

6

Bob
Moose

1968

2.74

2.22

7

Bob
Bruce

1964

2.76

2.23

8

Bob
Veale

1965

2.84

2.24

9

Bill
Singer

1967

2.65

2.24

10

Don
Sutton

1968

2.60

2.25

11

Mike
Cuellar

1966

2.22

2.28

12

Chris
Short

1964

2.20

2.28

13

Sam
McDowell

1965

2.18

2.29

14

Gaylord
Perry

1966

2.99

2.30

15

Dean
Chance

1964

1.65

2.31

16

Luis
Tiant

1968

1.60

2.34

17

Jim
O'Toole

1964

2.66

2.35

18

Whitey
Ford

1964

2.13

2.37

19

Gaylord
Perry

1968

2.44

2.37

20

Tom
Seaver

1968

2.20

2.38

21

Dean
Chance

1968

2.53

2.39

22

Bob
Gibson

1967

2.98

2.40

23

Don
Drysdale

1964

2.19

2.40

24

Gary
Peters

1963

2.33

2.41

25

Mike
Cuellar

1968

2.74

2.42

Notice that Gibson’s 1968 season, although the best, does
not dominate the way his actual ERA dominates. The next table shows the lowest
25 actual ERAs from the period.
Rank

Pitcher

YEAR

ERA

Pred

1

Bob
Gibson

1968

1.12

2.02

2

Luis
Tiant

1968

1.60

2.34

3

Dean
Chance

1964

1.65

2.31

4

Sandy
Koufax

1966

1.73

2.20

5

Sandy
Koufax

1964

1.74

2.16

6

Sam
McDowell

1968

1.81

2.53

7

Phil
Niekro

1967

1.87

2.68

8

Sandy
Koufax

1963

1.88

2.06

9

Joe
Horlen

1964

1.88

2.69

10

Dave
McNally

1968

1.95

2.92

11

Denny
McLain

1968

1.96

2.75

12

Bobby
Bolin

1968

1.98

2.60

13

Gary
Peters

1966

1.98

2.62

14

Tommy
John

1968

1.98

2.91

15

Sandy
Koufax

1965

2.04

2.18

16

Stan
Bahnsen

1968

2.05

2.71

17

Joe
Horlen

1967

2.06

2.93

18

Bob
Veale

1968

2.06

2.95

19

Jerry
Koosman

1968

2.08

2.80

20

Dick
Ellsworth

1963

2.10

2.62

21

Whitey
Ford

1964

2.13

2.37

22

Steve
Blass

1968

2.13

2.85

23

Juan
Marichal

1965

2.14

2.67

24

Don
Drysdale

1968

2.15

2.63

25

Vern
Law

1965

2.16

3.01

In predicted ERA, there are 24 pitchers within .40 or less
of Gibson. But in actual ERA, it is only one!. So using only pitcher determined
outcomes (strikeouts, walks and HRs allowed), brings Gibson back down to earth.
He is the leader, but he is not so far away from the rest of the pitchers.
Now that we have seen these results, lets check to see if
Gibson did indeed have a low batting average allowed on balls in play (BABIP)
in 1968. The table below shows Gibson’s BABIP for each year of his career along
with the BABIP of the entire Cardinal staff (including Gibson). Notice that his
lowest BABIP was in 1968 as well as the difference from the Card’s staff. 1968
was also the biggest difference.
YEAR

BABIPGibson

BABIPCards

Diff

1961

0.283

0.276

0.007

1962

0.249

0.272

0.023

1963

0.271

0.267

0.004

1964

0.272

0.275

0.002

1965

0.256

0.273

0.016

1966

0.240

0.267

0.027

1967

0.280

0.268

0.012

1968

0.230

0.264

0.034

1969

0.270

0.269

0.002

1970

0.299

0.293

0.005

1971

0.270

0.291

0.021

1972

0.263

0.277

0.014

1973

0.255

0.271

0.015

1974

0.272

0.274

0.002

1975

0.303

0.283

0.020

In some years Gibson had a lower BABIP than the Cards staff,
in other years, higher. But he definitely had a low BABIP in 1968 (some of the
numbers in the “Diff” column may look slightly wrong due to rounding). The next
table shows the lowest 25 BABIPs of the period.
Rank

Pitcher

YEAR

BABIP

1

Dave
McNally

1968

0.202

2

Joe
Horlen

1967

0.214

3

Wally
Bunker

1964

0.214

4

Joe
Horlen

1964

0.216

5

Luis
Tiant

1968

0.216

6

Phil
Ortega

1966

0.221

7

Denny
McLain

1966

0.221

8

Juan
Marichal

1966

0.221

9

Bobby
Bolin

1966

0.222

10

Dick
Hughes

1967

0.224

11

Carl
Willey

1963

0.224

12

Sonny
Siebert

1967

0.225

13

George
Brunet

1968

0.225

14

Sonny
Siebert

1968

0.225

15

Jim
Bouton

1964

0.226

16

Ernie
Broglio

1963

0.229

17

Lew
Krausse

1968

0.229

18

Bob
Gibson

1968

0.230

19

Rickey
Clark

1967

0.231

20

Pete
Richert

1966

0.231

21

Denny
McLain

1968

0.231

22

Jim
Bouton

1963

0.231

23

Ken
McBride

1963

0.233

24

Bobby
Bolin

1968

0.233

25

Moe
Drabowsky

1963

0.233

Gibson did not have the lowest BABIP, but he was #18.
If we try to predict Gibson’s ERA using regression analysis
and also include hits on balls in play, we will be able to predict his ERA much
more accurately. I ran a regression in which a pitcher’s ERA was the dependent
variable and his nonHR hits, walks and HRs allowed per 9 IP were the
independent variables (since I am using what happens on balls in play here, it
is not necessary to put stikeouts inevery strikeout means one less chance for
a hit and the number of hits is already accounted for in the model).
(2) ERA = 2.17 + 1.397*HR + .466*NONHR + .310*BB
The rsquared was .811, meaning that 81.1% of the variation
in ERA across pitchers is explained by the equation. The standard error is
.303. I then predicted each pitcher’s ERA using equation (2) and found how much
that differed from their actual ERA. It predicted Gibson to have a 1.49 ERA.
This is only .37 above his actual ERA, much more accurate than equation (1),
which was off by .90. But the point here is not to find which equation is most
accurate. The point is that once you include what happens on balls in play, we
get a much more accurate picture of Gibson’s performance. And in this case Gibson
was off by just 1.22 standard errors (.37/.303) while he was off by 1.92
standard errors with equation (1) (.90/.469). This supports the thesis that
Gibson was helped quite a bit by his low BABIP.
A few weeks ago a I posted an article about the best seasons
in something called “Fielding Independent ERA” or FIP ERA (see sources at the
end of this article). In that article I used a more sophisticated approach than
I used here. The lowest 25 FIP ERAs of this period are in the table below.
Rank

Pitcher

YEAR

FIP ERA

1

Sam
McDowell

1965

1.96

2

Bob
Gibson

1968

2.21

3

Sandy
Koufax

1963

2.23

4

Al
Downing

1963

2.25

5

Sandy
Koufax

1966

2.28

6

Bob
Veale

1965

2.30

7

Gary
Peters

1963

2.32

8

Sonny
Siebert

1965

2.32

9

Gaylord
Perry

1966

2.32

10

Sandy
Koufax

1964

2.38

11

Dick
Radatz

1964

2.39

12

Luis
Tiant

1968

2.39

13

Steve
Hargan

1966

2.43

14

Dean
Chance

1964

2.46

15

Mike
Cuellar

1966

2.49

16

Chris
Short

1964

2.50

17

Whitey
Ford

1964

2.51

18

Bill
Singer

1967

2.53

19

Sam
McDowell

1968

2.55

20

Sam
McDowell

1966

2.56

21

Bob
Bruce

1964

2.57

22

Bob
Moose

1968

2.60

23

Dean
Chance

1968

2.62

24

Jim
O'Toole

1964

2.63

25

Jim
Maloney

1963

2.67

Notice that Gibson is only second (the FIP ERA’s do not
completely correspond to predicted or actual ERAs mentioned earlier since all
ERAs in the FIP ERA study are normalized to a league with an ERA of about
3.70). The FIP ERAs here are also different because HRs allowed were adjusted
for park effects, something not done for the above analysis.
We can tell from the following stats that Gibson’s
performance in 1968 was not as far above his other seasons as ERAs alone would
indicate. The table below shows his strikeouts, walks and HRs allowed per
batter faced for each year in his career with 100 or more IP. 1968 is clearly
his best, but some other seasons rival it. In 1970, for example, his strikeout
and HR rates are very close to 1968. In 1967, his strikeout rate and BB rate
were similar to that of 1968. But 1970 was a much higher scoring season than
1968 with the NL ERA being 4.05. Gibson’s fielding independent stats in 1970
are almost as good as they were in 1968.
YEAR

SO/BFP

BB/BFP

HR/BFP

1961

0.181

0.136

0.014

1962

0.215

0.109

0.016

1963

0.188

0.100

0.017

1964

0.206

0.080

0.021

1965

0.219

0.092

0.028

1966

0.201

0.074

0.018

1967

0.209

0.061

0.014

1968

0.231

0.059

0.009

1969

0.212

0.083

0.009

1970

0.226

0.076

0.011

1971

0.180

0.081

0.014

1972

0.186

0.081

0.013

1973

0.180

0.076

0.015

1974

0.124

0.105

0.023

1975

0.120

0.132

0.020

The next table shows his FIPERAs for the years 19611974
(season when he had at least 150 IP).
Year

FIP ERA

1961

3.08

1962

2.56

1963

3.31

1964

3.15

1965

3.47

1966

3.08

1967

2.69

1968

2.21

1969

2.46

1970

1.96

1971

3.03

1972

2.90

1973

3.12

1974

4.87

As mentioned earlier, these FIP ERAs are all normalized for
a league with about a 3.70 ERA. According to this, Gibson was better in 1970
than in 1968. That is, taking park effects into account to adjust HRs, using
only pitcher controlled stats and comparing to the league average shows his
1970 season to be even better. This, too, suggests that 1968 was helped quite a
bit by a very low BABIP. The big difference between the two seasons was his
BABIP of .230 in 1968 and his .299 BABIP in 1970. The 1968 BABIP was far below
the team BABIP while his 1970 BABIP was above the team BABIP.
I also broke down his performance into RISP and nonRISP
situations to try to understand how his ERA could have been so low. He allowed
a batting average of .184 overall but just .141 with RISP (and .193 in nonRISP
situations). To see if this made any difference, I ran a regression with ERA as
the dependent variable and onbase percentage (OBP) and slugging percentage
(SLG) were the independent variables. That predicted Gibson to have an ERA of
1.25 (just using pitchers from 1968). Then I broke down OBP and SLG into RISP
and nonRISP situations. The resulting regression equation predicted Gibson to
have an ERA of 1.13. So his RISP performance also helped a little in making his
ERA so low since the regression that took RISP into account was more accurate.
His career average allowed overall was .228 while with RISP it was .219. Those
two are pretty close, indicating that Gibson probably did not have any special
ability with RISP. He just happened to do very well in those situations in
1968.
I also took the natural log of ERA in one of the regressions
in case ERA had a nonlinear relationship with the other stats. Doing this did
not improve the results.
There is one other issue with the fielding in 1968. It
appears that Gibson got a little lucky in 1968 with more balls in play than
average being turned into outs. Perhaps the fielders were playing better or
trying harder behind Gibson that year than they were for the other Cardinal
pitchers. But Gibson actually gave up more unearned runs than would be expected
as compared to the entire Cardinal staff. The staff ERA was 2.49 or 1.37 above
Gibson. But if we include all runs, Gibson gave up 1.45 runs per 9 IP while it
was 2.87 for the whole staff or 1.42 higher than Gibson. So by adding in
unearned runs, the difference between Gibson and the team grows. Gibson’s runs
per 9 IP was 29.46% above his ERA while
for the whole staff it was 15.26% higher. So Gibson was hurt more by unearned
runs than the whole team, indicating that his fielders hurt him. Perhaps they
were hustling more and simply got to more balls, leading to more errors. Maybe
official scorers called more errors than expected to protect Gibson’s ERA (it
is true that Gibson’s runs per 9 IP is .33 higher than his ERA while it is .38
for the whole staff, possibly showing that Gibsons was hurt less by unearned
runsbut with fewer base runners allowed, any given error should have hurt him
less so a .33 increase is proportionally worse for him than a .38 increase was
for the whole team).
Sources:
The Complete Baseball Encyclopedia from Lee Sinins
The
Best Fielding Independent Pitching Seasons From 19202005