Why Did Home Runs Surge Throughout The Minors In 2021?

Image credit: Griffin Conine (Photo by Paul Gierhart)

The home run surge that swept through Triple-A in 2019 was apparently contagious. In 2021, it spread to the other three levels of the full-season minor leagues.

But the records Triple-A teams set in 2019 had a clear explanation—the baseball changed. There is no easy answer for why teams were all of a sudden hitting the ball out of the park at much higher rates in the lower levels of the minors.

When Major League Baseball decided to bring the MLB ball to Triple-A in 2019, it sparked a record-breaking season for home runs around the minors. Balls flew out of Triple-A parks at record rates while the other levels of the minors, which used the standard minor league ball, kept hitting home runs at rates consistent with what had been seen in previous years.

This year, the balls kept clearing the walls, but in ways that may have been somewhat unexpected. In 2021, the home run surge was focused on every level other than Triple-A.

In 2021, the home run rate at Triple-A dropped off a little from its previous high. Double-A, High-A and Low-A all saw significant power spikes even though the type of ball they used remained unchanged.

At the Triple-A level, home runs dropped from 1.37 per game to 1.24 per game. That’s still dramatically higher than the 0.71 to 0.87 home runs per game range the level saw from 2016 to 2018, but it’s still 90% of the home run rate in 2019.

But at every other level of the full-season minors, teams hit home runs at rates that seem astonishing when compared to 2019.

• At Double-A, the home run rate was up 47%, from 0.75 per game in 2019 to 1.10 this year.

• At Low-A, the home run rate was up 33%, from 0.62 per game in 2019 to 0.82 this year

• At High-A, the home run jump was a massive 65%, from 0.64 per game in 2019 to 1.06 in 2021

Those levels are using the same standard minor league ball they have used for years.

There are likely a variety of factors at play. Thanks to the reorganization of the minors, multiple leagues shifted levels. The High-A Florida State and California leagues became the Low-A Southeast and West leagues. The short-season Northwest League morphed into the High-A West, while the Low-A Midwest League became High-A Central. The Low-A South Atlantic League and High-A Carolina League were reshuffled to form the new Low-A East and High-A East leagues.


So in many cases, the ballparks and environments within which teams play have changed. The 2021 minor league season also didn’t start until May, which meant that the power-sapping cold of April did not play a factor in this year’s season. And rules changes, most notably automated balls and strikes in Low-A Southeast, led to some alterations in the environment as well.

But none of that explains the entirety of the jump in home runs. The teams in the Double-A leagues largely played in the same parks they did in 2019, and home runs in those leagues increased at similar rates. It’s fair to suggest that the emphasis on hitting for more power, and accepting a rise in strikeout rate to go with it, likely also played a role.

The strikeout rate at all four levels was higher than it was in 2019, with the jump ranging from 4.4% in Triple-A up to 16.3% in High-A. At all but the Low-A level—where robo umps led to a massive increase in walk rate in Low-A Southeast—the walk rate increases were right in line with the strikeout rate increases.

As far as run scoring, the power increases in the lower levels meant that for the first time in years, run scoring was relatively equivalent across all four levels. Runs per game at Triple-A dipped from 5.52 in 2019 to 5.11 in 2021. Double-A runs per game increased from 4.10 to 4.72. High-A jumped from 4.15 to 5.06. And Low-A skyrocketed from 4.28 to 5.27.

Across the full-season minors as a whole, the average hitter hit .247/.334/.406. The average game saw 5.04 runs per team per game, with 3.84 walks and 9.62 strikeouts.

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