No feat in American sports captures the imagination quite like the home run. The act of sending a baseball soaring into the sky, over the fence and into the bleachers represents the pinnacle of strength and power.

The homer earned that status in part because of its rarity. From 1900 through 2015, Major League Baseball averaged 1.4 home runs per game, meaning that a fan showed up to the ballpark not expecting to see both teams hit one. But in the past four seasons, that number has jumped to 2.5 homers per game, an offensive...