Who was the greatest left-handed pitcher in history? My money is on Lefty Grove. This issue came up in a Joe Sheehan piece titled By Any Measure: It's no tall tale: The Big Unit was the greatest lefthander of them all. SABR members were told about it in a recent email and it got mentioned in a Seattle Post-Intelligencer blog. So here is my take on the issue.
In the table below, I summarize each pitcher's career. Here is what the abbreviations mean:
WS = Win Shares (created by Bill James)
WAR = Wins Above Replacement (from Sean Smith)
PW = Pitching Wins (from Pete Palmer via Retrosheet)
ERA+ = ERA adjusted league average and park effects (from Baseball Reference)
Grove does very well. WS might take into account clutch performance or high leverage situations. Grove pitched in relief in about 25% of the games and had alot of saves for his era. This could be bumping up his WS. Koufax and Johnson did not pitch much in relief. But Grove has such a big lead, it might not matter.
Grove pitched until he was 41 and Johnson until he was 45. If I drop Johnson's last 4 seasons, his ERA+ is 151, just slightly ahead of Grove. But then Johnson gives up about 5 WAR and over 500 IP.
The next table shows the best 5 consecutive seasons for each pitcher. Peak value should be included in any evaluation along with career value. Again, Grove looks very good.
This might not be fair to Johnson. For whatever reason, modern pitchers don't pitch as many innings as those in the past. Grove's 5 highest IP seasons add to 1,421. For Koufax it is 1,447 and for Johnson it is only 1,285. If we increased his totals in the above graph by about 10%, he would still trail Grove.
Now the best 3 consecutive seasons.
Grove looks very good again. If we gave Johnson a 10% bump, he would pass Grove, but in only one measure, WAR, and not by much.
We should also look at how they each did in the pitcher cotrolled stats. In the next table, HR shows how well they each did in preventing HRs. Grove gave up 43% fewer HRs than the average pitcher during his career (that is what the 143 means, from the Lee Sinins Complete Baseball Encyclopedia). The number in parantheses is where each pitcher ranks among lefties with 2,000+ IP since 1920.
SO/BB is strikeout-to-walk ratio relative to the league average. The 211 for Grove means his ratio was 2.11 times the league aveage.
This looks very good for Grove. If I dropped the last 4 seasons for Johnson, he gets 122 for HR and 180 for SO/BB, still well below Grove.
The next table shows the same stats for each player over what was probably their best 5-year stretch. For Grove it was 1928-32, for Koufax it was 1962-66 and for Johnson it was 1998-2002. Grove again dominates.
During these years, Grove's park allowed about 50% more HRs than average, Koufax's about 40% fewer and Johnson's was about average. Grove had an ERA+ of 174, Koufax 169 and Johnson 178. A slight edge for Johnson, but I don't think enough to overcome Grove's big leads in so many other cases.
If we simply compare the relevant stats to the league average, Grove seems to have performed better than the other two whether we consider career value or peak value.