Upon Further Review examines Brian Bannister’s extreme day/night split. He’s a Cy Young winner under the sun, a replacement player at night. A reverse vampire, if you will. They don’t offer an explanation, but suggest the Royals find a way to pitch him during the day as much as possible.

I think they are wrong here, however:

I ran the program one million times. Assuming a pitcher is a .500 pitcher, the odds of randomly having 15+ wins in 19 games is .0096 – or just under 1% of the time.
I did the same thing based on 38 night games. What percentage of the time would a .500 pitcher only have 13 (or less) victories? The answer is .0364 – or 3.6%.
Therefore, what are the chances that both could be true at the same time? Well, that’s as simple as multiplying them times each other. Thus, the probability that Bannister could be 15-4 and 13-25 purely by random chance is .0003503 – or roughly 3 one-hundredths of a percent. In other words, there is virtually no chance that it is by chance.

Wins is the wrong thing to measure. If the Royals had a great offensive team, he might have a same ERAs and a much better record at night. Looking at on-base average allowed might make more sense.

Bill James wrote an article in an early abstract about an advantage power pitchers acquired at night, but over the years improvements in lighting technology may have wiped that away. As Bannister is not a power pitcher, we wouldn’t expect a night time boost, but we wouldn’t expect a day time one, either.

Maybe it’s as simple as Bannister being a morning person. Don Baylor, when he was coaching the Brewers, lectured a batter about his terrible day stats compared to his night stats. Baylor told the player that it was the result of late night partying, and told him to get some sleep before day games. If Bannister is the type of person (and I’m one) who likes to get up early, he may just be tired when a night game comes around.