Fivethirtyeight breaks down how recent changes to seams of baseballs manufactured for the MLB are leading to a decrease in drag coefficient. The decreased drag coefficient leads to decreased air resistance in flight and consequently could be at least partially responsible for the homerun spike we are seeing this season.
More information in the Fivethirtyeight article here: https://fivethirtyeight.com/features/in-mlbs-new-home-run-era-its-the-baseballs-that-are-juicing/.