Lots of variables of course, but…

- If the pitcher walks three in a row, their inning could be done.
- If the defense is the cause of an extended inning, don’t leave the pitcher in for more than 5 runs or you are just wasting them.
- If a pitcher has a second ~30 pitch inning, it’s not their day.
- If there aren’t any swing and misses and a hit parade has started (three or more consecutive hits), it’s not their day.

I would generally look more at pitches thrown and bats missed, more than runs. It will also depend upon age level: a 10U kid can give up 8 runs in an inning and forget about it prior to their at bat. An effective 18U kid can’t have an ERA above 4.