I'm sure all of us have seen near-misses at games... a fan isn't paying attention as a foul ball screams past, a first base coach gets nearly decapitated by a line drive. This book seems to bring it all home. (It turns out that errant line drives and fastballs aren't the most frequent culprit in on-field deaths.)
Here's the most improbably tragic story:
During a 1949 amateur game in Florida, the third baseman, shortstop, and second baseman were all killed by a single lightning bolt, which struck the backstop, then shot around the infield as though completing a double play.
The book obviously wont appeal to everyone, but at least the Slate review is worth a look.
Death at the Ballpark: A Comprehensive Study of Game-Related Fatalities of Players, Other Personnel and Spectators in Amateur and Professional Baseball, 1862-2007 by Robert M. Gorman and David Weeks