A few days ago reader Devon Young wrote me that Greinke would have an historically low ERA going into July 24, the next day he was scheduled to pitch. I did it a little differently, since the day of the year doesn’t really indicate the length of the season very well. I went with days into the season, which at this point is 111. Devon also looked at the best ERA in the majors in a given season, I’m listing them all.
Normally I would just go back to 1969, since lowering the mound that year was the last physical change that had a direct influence on pitchers. It was the 1968 season that led to that change, so I’ve included that year as well. Pitchers must have 100 IP, so that helps eliminate the strike seasons.
| Season | Pitcher | Games | Earned Runs | Innings | Earned Run Average |
| 1968 | Bob Gibson | 21 | 20 | 187.7 | 0.96 |
| 2015 | Zack Greinke | 19 | 19 | 131.3 | 1.30 |
| 1968 | Luis Tiant | 23 | 27 | 183.7 | 1.32 |
| 2005 | Roger Clemens | 20 | 21 | 135.0 | 1.40 |
| 1971 | Vida Blue | 24 | 32 | 204.3 | 1.41 |
| 1974 | Gaylord Perry | 21 | 31 | 189.3 | 1.47 |
| 2000 | Pedro Martinez | 16 | 20 | 121.0 | 1.49 |
| 1998 | Greg Maddux | 21 | 28 | 161.0 | 1.57 |
| 2010 | Josh Johnson | 20 | 24 | 134.3 | 1.61 |
| 1997 | Roger Clemens | 20 | 28 | 155.3 | 1.62 |
| 1972 | Gaylord Perry | 27 | 42 | 232.3 | 1.63 |
| 1968 | Sam McDowell | 23 | 32 | 174.3 | 1.65 |
| 1995 | Tim Wakefield | 17 | 24 | 131.0 | 1.65 |
| 1997 | Pedro Martinez | 18 | 26 | 140.0 | 1.67 |
| 1994 | Greg Maddux | 21 | 32 | 168.0 | 1.71 |
| 1985 | Dwight Gooden | 22 | 33 | 170.7 | 1.74 |
| 1968 | Jerry Koosman | 22 | 32 | 163.3 | 1.76 |
| 1998 | Al Leiter | 16 | 21 | 107.7 | 1.76 |
| 1969 | Steve Carlton | 19 | 30 | 150.0 | 1.80 |
| 2008 | Justin Duchscherer | 16 | 22 | 108.7 | 1.82 |
| 2014 | Adam Wainwright | 19 | 28 | 138.0 | 1.83 |
So Gibson was under 1.00 at this point, despite pitching many more innings. The number of innings pitched by the leaders in the late 1960s and early 1970s boggles the mind.
Most of the pitchers on this list were extremely good for their careers, many Hall of Famers or potential Hall of Famers. The only one who really sticks out is Justin Duchscherer, who moved from the bullpen to the rotation in 2008, but injuries and illness pretty much ended his career after that season.
So can Greinke beat Gibson’s 1.12 ERA of 1968? Greinke likely has 12 starts left. If he averages 7 1/3 innings per start (he’s averaging a little under 7 right now), he would pitch 88 more innings. At that level, he would need to allow no more than nine earned runs for a 1.11 ERA. Breaking Hershiser’s consecutive scoreless inning streak would help.