Major League Baseball used some baseballs from the 2018 regular season in the 2019 playoffs, according to a study by Dr. Meredith Wills in The Athletic.
The 2019 regular season's massive surge in home runs dried up during last year's playoffs. Wills examined a sample of baseballs used in the 2019 postseason and found, based on their Batch Designation Codes, that several had been intended for use in the 2018 season, including all five of the World Series balls she disassembled of the seven in the sample.
"Contrary to previous statements (from the league), testing showed that balls provided for 2019 postseason games were a mixture from the 2019 and 2018 regular seasons," Wills wrote. "Why would this be the case? A new theory has emerged - one that comes down not to 'de-juicing,' but to simple supply and demand."
Wills believes the league used balls from 2018 because of inventory issues, which she suggests were caused in part by authenticating more game-used balls for sale and in part by the fact that Triple-A began using MLB baseballs in 2019. However, she doesn't understand why the league "continued to maintain that all 2019 postseason balls were taken from 2019 regular-season stock."
Wills told SNY's Danny Abriano that she doesn't expect significant changes to the 2020 baseballs, though she guessed that they might be less slick, since it would be realistic to alter the texture on a quick turnaround.
"In theory, they might still be producing them," Wills said. She added, "Based on that narrow window - assuming they had a few months to take data from the previous season and then find a way to use it for the subsequent season ... that means that really major changes just aren't possible."