A Flatliner in tennis is a player who often hits flat shots with little spin.
These shots travel low over the net and move fast through the air. Flatliners can hit the ball deep into the court with great accuracy.
This style of play can be very effective on fast surfaces like grass.
Lindsay Davenport and Andre Agassi are famous examples of flatliner players. Their powerful, flat groundstrokes helped them win many matches and Grand Slam titles.