Following on from last post–how lucky are we to have two perfect games in a matter of weeks?!–I tried to figure out why perfect games are becoming more common while regular no-hitters are becoming even less so (see this New York Times article for more).
The two major factors that turn a perfect game to a no-hitter are walks and errors. (These are not the sole factors; I found at least two no-hit, no-walk, no-error games since 1920 made imperfect by hit batters!) But I graphed the average number of walks and errors surrendered by pitchers throwing no-hitters, by decade. Fielding has improved since the ’20s, evidently. Walk rate has been more erratic but decreasing since the 70s; more free swingers today? You can see how this changes the numbers of perfect games.
Please note that Retrosheet did not have all the results; these averages exclude one no-hitter from the 1940s and five from the fifties, and that’s why I started in 1920. Edit: found more results to fill in the ’40s and ’50s. This smooths out the graph a little; the “walks” line jumped down a bit without taking Cliff Chambers’ eight-walk performance into account.
Other interesting results: two of the three Joneses to throw no-hitters were named Sam, but only one was Sad Sam Jones. (The other, Bumpus Jones, threw his in 1892 and has been excluded from this analysis.) Two pitchers in the ’70s had no-hit, no-walk games but neither were perfect. Blame the fielders? Well, no; all three of the relevant errors came from the pitchers themselves, and one of them was advancing a runner hit by a pitch. Bill Monbouquette is an awesome name, and Nolan Ryan was really good.