Probably every baseball fan knows who Sandy Koufax was and that he was a great pitcher back in the 1960s. Some evidence shows that he was great. Here are the best ten ERAs in all of baseball from 1962-1966 (the years Koufax pitched in Dodger Stadium) for pitchers with 810 or more innings pitched:
(the 810 IP works out to 162 per season). Pretty impressive lead for Koufax. But Dodger Stadium favored the pitchers. Here are its park factors for the 1962-66 seasons from the STATS, INC. All-Time Baseball Sourcebook:
The 82 for the run factor in 1962 means that the number of runs scored in Dodger Stadium was only 82% of the National League average. The number in parentheses indicates Dodger Stadium's rank in how much it favored the pitchers. That is, the 82 for run factor in 1962 was the lowest in the league. The 84 in 1963 was tied. It is pretty clear that Koufax pitched in a great park for pitchers. To adjust for park factors, the table below shows the NL leaders in RSAA from 1962-66. RSAA comes from the Lee Sinins' Complete Baseball Encyclopedia. Here is the definition: "RSAA--Runs saved against average. It's the amount of runs that a pitcher saved vs. what an average pitcher would have allowed." It is also park adjusted, so that pitchers who pitch in good hitter's parks get an adjustment upward in their RSAA, and vice-versa. A below average pitcher will have a negative RSAA.
Koufax has a pretty big edge over the number two man, Marichal, even with the park factors taken into account (the factors used in the Lee Sinins' Complete Baseball Encyclopedia are not necessarily the same as those in the STATS, INC. All-Time Baseball Sourcebook). Of course, this period covers Koufax's prime and may not cover the exact prime years of anyone else. This was definitely not the best five-year performance any pitcher ever had (see my article from last week called The Best Five-Year Pitching Performances).
Adjusting for park factors does not always tell the whole story. Some pitchers benefit disproportionately from their parks. Koufax had a 1.37 ERA in home games over this period while it was 2.57 in road games (all home and road data from Retrosheet). The home/road ratio was .533. That means that he allowed only about 53.3% as many runs at home as he did on the road. Looking at Table 2, we can see that the normal rate was about 80% for Dodger Stadium. So yes, Koufax did benefit alot more than normal from his park. Koufax also allowed 55 HRs in road games while facing 2,681 batters for a rate of 2.05%. At home, it was 34/2,714 for a rate of 1.25%. Since 1.25/2.05 is about .61, it means his HR rate at home was 61% of what it was on the road. The average HR factor for Dodger Stadium from 1962-66, weighted by Koufax's IP in each season, was 59.35, just a little under 61. So Koufax, when it comes to HRs, benefited from Dodger Stadium, but just a little less than average. He had a 5.31 strikeout-to-walk ratio at home and 3.97 on the road.
Over the 1962-66 period, the average ERA in home games was 3.40 and 3.76 on the road for all NL pitchers. So the home/road ratio was .904. That far exceeds Koufax's .533. Koufax's differential of 1.20 was far higher than the normal differential of .36. Another way to look at this is to look at the ERA at Dodger Stadium vs. the ERA compiled in Dodger road games. All pitchers (minus Koufax), both Dodgers and their opponents, had an ERA of 3.10 in games at Dodger Stadium. In road games, it was 3.69. So the ratio is .84 (3.10/3.69). Again, that is far higher than for Koufax. The differential of .59 is only half of what it was for Koufax.
I also compared Koufax to some of the other good NL pitchers from this time by using their stats in neutral parks. For example, I looked at how Koufax and Juan Marichal did outside of both Dodger Stadium and Candlestick Park where the Giants played. The table below shows how Koufax compares to Marichal, Bob Gibson and Jim Bunning (only over the years 1964-66 since those were the only years Bunning was in the NL while Koufax pitched in Dodger Stadium).
These other three pitchers put up numbers comparable to Koufax while pitching in neutral parks. But I don't think it is clear how this should change our ranking or perception of Koufax. These other guys were good, if not great pitchers, too. And this analysis, of course, looks at less than half of Koufax's IP in this period. On the other hand, it suggests that Koufax might not have been as far above his competition as we normally think.