Actually, I have some pretty reliable reference material that says that it was Mike 'ONeill, St. Louis Cardinals, 6/3/1902. Whenever I do research for a question and you guys come up with other answers that I haven't seen (and you seem pretty sure about them), I always like to do additional research to verify that my answer is indeed correct. Especially when 2 or more members have the same answer and seem reasonable sure of it. In this case I got a response from a very reliable source that said this:
Michael:
Thank you for writing (name removed

) with your research
question. According to THE BASEBALL TIMELINE, by Burt Solomon (2001), Mike
O'Neill did hit the first pinch-hit grand slam in National League history,
on June 3, 1902, off Togie Pittinger. I have found no mention in the
timeline of any earlier pinch-hit grand slams in other major leagues.
So in
the absence of evidence to the contrary, that appears to be the first
pinch-hit grand slam in major league history as well. (Pinch-hitters were
seldom used in the 19th century.) The TIMELINE also lists Marty Kavanaugh
with the first pinch-hit grand slam in AL history, on September 24, 1916.
I hope this information helps. If we can be of further assistance, please
let us know.
Signed,
(name removed)
I try hard to verify that my answers have integrity and my questions are not confusing by being ambiguous or too obscure. Most of my questions are not designed to trick as much as they are designed for everyone to think and learn a little about baseball history.
I hope you enjoy!
Well Look who has come to the cafe, It's Mr. Met!