Just a quarter-century ago, Major League Baseball was ravaged by a strike that canceled the 1994 World Series and left the future of the national pastime in doubt. One thing brought the game back from the abyss: Mark McGwire and Sammy Sosa’s pursuit of a record 62 home runs, a race that captivated fans in a way that no longer seemed possible.

Now, barely 20 years later, baseball faces another crisis that threatens its place in the fabric of American culture. The home run, the thrilling feat that once saved the sport, might...