Much has been written about the “tape measure” home runs hit by such baseball sluggers and Mickey Mantle and Babe Ruth. But how far can anyone throw a baseball?
That question was answered in Cincinnati on October 12, 1910. An outfielder named Sheldon LeJeune threw a baseball 426 feet, 9 1/2 inches. It remains the longest baseball throw ever measured.
From The Giant Book of More Strange But True Sports Stories by Howard Liss. Illustrations by Joe Mathieu.
https://en.wikipedia.org/wiki/Glen_Gorbous
In the latest of example of Liss not having the interwebs available to him, it looks like LeJeune’s record was broken by Glen Gorbous (linked above) in 1957. This book was published in 1981.
For a point of reference, Gorbous’ throw went the distance from the far right field corner of the stadium to the far left field corner.