["Contrary to popular belief because of his nickname..."] --- This reads a trifle awkwardly. I'd suggest "Contrary to popular belief (caused by his nickname)..."
["I walked behind more mules than I walked batters – and that's saying a lot," he compared his childhood with his career.] --- "Compared" is an awkward stand-in for "said". I'd recommend a slight tweak: [he later reflected, comparing his childhood with his career.]
Probably worth blue linking to smokehouse - urban readers might not know the term.
It's a minor point, but you link starts the second time you use it ("...a 3.65 ERA in 30 starts..."); by Wikipedia convention, it should be the first occurrence of the term that's linked ("...Two starts later, on May 2...")
[he held the Phillies to run one] --- Should be "one run".
Mizell's time in Cuba should probably be in its own section, as it seems to have occurred after his military service.
My first thought was to wonder why he went to Cuba instead of straight back to St. Louis. But perhaps the MLB season had already ended by the date of his discharge? Worth a line of explanation.
[He had a 3.62 ERAfor the Cardinals] --- Missing a space.
[We've got at least three pitchers capable of winning 20–Herm Wehmeier, Sam Jones...] --- After the 20, I think it should be a hyphen (-) rather than an en dash (–).
[His season high for strikeouts this year] --- It seems more natural to say "that year".
The title of retirement doesn't quite fit this section, which covers several other aspects of his life outside baseball and politics. "Personal life", maybe?
Minor issues only - I'll await your response to the above points
Issues now dealt with - I'll give the article GA status. Good work, and thank you for the interesting read. Harper J. Cole (talk) 18:53, 17 May 2021 (UTC)[reply]