From the Super Mario Wiki, the Mario encyclopedia
The Hand-Power Save is a Defensive Power Shot that Clay and Ace can use in Mario Tennis: Power Tour, and L1 ESP is required to obtain it. Willy also uses this shot in the Island Open, and must be defeated in the finals to unlock Instinct Drill, the only source of PS ESP to acquire it with. Upon use, the user will send out a magic hand to brings the ball back to them.
"A save that brings in balls from far away using hand power."