Today in Baseball History: 15-year-old Joe Nuxhall becomes the youngest player in MLB history

In 1944, at the height of American involvement in World War II, MLB teams were faced with an unusual problem: They were running out of players. Stars and journeymen alike had rushed to enlist in the armed forces, leaving many rosters scrambling to field a full squad -- including the Reds, who had taken to scouting Ohio looking for possible contributors.
One player they wanted was Orville Nuxhall, a semipro pitcher from nearby Hamilton. But Nuxhall wasn't interested; he had five kids, and wanted to put his family first. Luckily for Cincy, though, it just so happened that part of that family was a 14-year-old boy named Joe with a live left arm. Reds scouts liked what they saw from the younger Nuxhall, and on Feb. 18, 1944 -- after waiting for his high school basketball season to end -- they signed him to a professional contract. 

Cincinnati still wasn't planning on making much use of its new arm, though. Joe was with the team on Opening Day (after getting permission from his high school principal), but for weeks he rode the bullpen bench -- until June 10, just a few weeks before Nuxhall's 16th birthday, with the Reds getting routed by the first-place Cardinals.
With the score 13-0 in the ninth inning, Cincy just needed someone to soak up the last three outs. So manager Bill McKechnie called on Nuxhall, making him the youngest player to ever pitch in Major League Baseball, a record that still stands today. Sadly, things didn't go too well that day: After retiring the first batter he faced on a groundout, Nuxhall gave up five runs on five walks and two hits, and a couple days later he was sent down to the Minors. Which, all things considered, isn't too surprising:
I was pitching against seventh, eighth and ninth graders, kids 13 and 14 years old. All of a sudden, I look up and there's Stan Musial ... It was a very scary situation.
Nuxhall was much more than just a historical footnote, though. He decided to stay at home in 1945 and finish high school, but he eventually rejoined the Reds, and after five years spent in the Minors, he was back in the big leagues in 1952. He'd pitch the next eight years for Cincinnati, even earning All-Star honors in 1955 and 1956 and retiring with a 3.90 ERA.