Kelly used the practice of throwing into a net during MLB's shutdown to work on his four-seam fastball, Rowan Kavner of Dodger Insider reports.
Per Statcast, Kelly threw his four-seamer 28 percent of the time in 2019, a marked dropoff from the 49.9 percent frequency on which he threw the pitch the previous season. The right-hander attributed the decrease to mechanics, explaining, "At the time before all this happened, I was essentially throwing a one-finger fastball. My index finger was coming off the heater. I was losing spin efficiency." Each of Kelly's fastballs in Thursday's intrasquad game were four-seamers, and given the positive results, it's logical to expect his use of the pitch to revert closer to his career norm this season.