By "long" delay, I mean an hour or more.
On one hand, a pitcher that has pitched two or three innings, and is interrupted by rain gets a chance to rest.
On the other hand, perhaps a pitcher has warmed up, and gotten into a "rhythm." Then perhaps the delay "undid" all this work.
Has a pitcher been likely to pitch the same way after a rain delay as before? Suppose there is more than one rain delay in the game. Has it been disruptive to most pitchers?
I was think in terms of last night's game, San Diego vs. Pittsburgh. Why did San Diego relieve its starter after two innings and an almost two hour rain delay, when he had given up no runs?