With the PGA Tour’s one-week offseason now in the rearview, some players are already tinkering with new gear or playing styles in the first week of the new season. Count Phil Mickelson among them.

Orlando, Fla.— Brian Tennyson remembers the last round of the 2019 British Amateur Championship at Scotland’s fabled North Berwick Links. He hit every par 5 in two, drove one par-4 green and had ...