Question: How would I hit an underhand topspin serve?
Answer: You can hit this serve using a stroke very similar to whichever topspin forehand groundstroke style you like best. The Western style,
grip and all, will give you the heaviest spin. For the Western style, toss the ball around head high, to your right, and toward the net 1-2 feet. Let the ball drop around 1.5 feet, then brush sharply up the back of the ball with as much swing speed as possible. Semi-western or Eastern styles will use a less forward toss and a lower point of contact.

