13 letters It "cannot stand" per 1-Down ... or a hint to 20-, 25- and 47-Across Answer: AHOUSEDIVIDED
13 letters Once-common baseball events ... and a hint to 16-, 24-, 46- and 57-Across Answer: DOUBLEHEADERS
13 letters The starts of 20-, 29-, 36- and 46-Across, e.g., when repeated quickly in order Answer: TONGUETWISTER