Power Shot (Offensive Power Shot)
From the Super Mario Wiki
The Power Shot is an Offensive Power Shot used in Mario Tennis: Power Tour by Roy, making it one of the first Power Shots used by opponents in the game's story mode. It requires 1 PS Muscle to unlock, and upon activation the user will absorb energy with their racket and hit the ball to the opposing side of the court. If an opponent returns this, they will be knocked back a bit.
This shot has a powered-up version called the High-Power Shot.
"A powerful shot that sends opponents flying."