Explanation From Original OP:

In 1944, the U.S. Army experimented with the T13 "Beano" grenade, designed to mimic the size and weight of a baseball. The logic of the Army was simple: most American soldiers grew up throwing baseballs, so muscle memory would improve throwing accuracy and distance in combat.

It even had an impact fuse, meant to detonate upon hitting the target, much like a perfectly aimed fastball.

Unfortunately, field tests showed it that the weapon was temperamental. Several accidental detonations later, the project was quietly cancelled.

Turns out not every soldier was major league material.

Additional note - the US would try another experiment like this in the 1970s, but this time with anti-armor grenades and footballs. It would be cancelled because the weight distribution in throwing is not the same as a fucking football.