The home run rate in Major League Baseball spiked dramatically in the second half of the 2015 season and has remained on an upward trajectory every since. As a result, we are on pace to shatter the all-time single season home run record in 2017 by over 300 homers.

Many people have asked why the home run rate has spiked and many potential answers have been offered. Among them are explanations which credit batters who swing harder, with greater uppercut swings, pitchers who throw harder, which could correlate with farther-hit balls when contact is made as well as other factors.

But an obvious explanation is a juiced ball. There is a long and rich history of changes — even slight changes — to baseball composition leading to dramatic increases in offensive levels. The dead ball era ended, in large part, because different wool was used beginning in 1919. The National League changed balls in order to intentionally boost offense in 1930 and it worked almost too well. There was a change of baseball manufacturers in the late 1970s which led to a mini spike. 1987 was the year of the so-called “rabbit ball.” That was never fully explained, but there are strong suspicions that Major League Baseball messed with the ball that year.

Many have looked at the recent surge in home runs and have tried to determine whether the baseball had been juiced. Most notably, Ben Lindbergh of The Ringer and Rob Arthur of FiveThirtyEight studied the matter last year. They concluded that the ball had not been altered. Later Major League Baseball said that its own research showed no changes to the ball, though they did not release their data for outside scrutiny. The mystery remained.