Offensive Power Shot
From the Super Mario Wiki
An Offensive Power Shot can be used by any character in Mario Power Tennis. The Offensive Power Shot makes the ball more difficult to receive, and receiving it gives hindering effects. For example, when Bowser's Offensive Power Shot is hit by any receivers, the receiver is pushed back by the massive force of the flaming ball. Other Offensive Power Shots can also make the player move slow for a short amount of time. These added effects are negated if receivers use their Defensive Power Shot.