At 240 pages, Major League Baseball's rule book is dense, and it is only growing denser. Last winter alone, the league added three new rules and amended six others—and that doesn't even count the two rules it has amended since this season began.

But for all its love of new legislation, MLB has shown little inclination to delete rules that have long ceased being relevant. As a result, the rule book has become baseball's version of the tax code, dotted with obscurities and oddities whose existence are unknown even to many players...