A reader emailed me this question:

"Who is the only player to hit an Inside the Park Grand Slam pinch hit Home Run and have it be the only Home run of his career?"

Well, I didn't know the answer, and haven't yet been able to verify that it happened that way (maybe someone can confirm this in the comments). But assuming that there is, in fact, precisely one such player, I think I found the answer.

This link lists the 12 major leaguers to hit both a pinch hit grand slam and an inside the park grand slam in their careers:

Randy Winn is the 12th major-leaguer, third in the past 50 years, to hit an inside-the-park grand slam (Oct. 3, 1999) and a pinch-hit grand slam (April 4). The others, according to SABR home run analyst David Vincent: Mike O'Neill, Beals Becker, Cy Williams, Marty Kavanagh, Rogers Hornsby, Harvey Hendrick, Les Bell, Hack Wilson, Pete Milne, Tim McCarver and Cesar Cedeno.

(A purportedly complete list of inside the park grand slams is here).

Of the 12, precisely one player had just one career home run: Pete Milne of the 1949 New York Giants. Milne batted 29 times in 31 games for the Giants that year while making just one appearance in the field, so it stands to reason that he was used mostly as a pinch hitter. (The list above identifies the date of his grand slam as April 27, 1949, a game the Giants won 11-8 over the hated Dodgers, so it's not surprising that it won him a job as a pinch hitter). So that appears to be the answer.