Originally Posted by TheCheese
Watch again. Federer doesn't hit flat forehands. He hits topspin forehands with a flat trajectory at times. People at home are constantly amazed how these pros are able to hit such flat shots without missing. They aren't threading the needle on every shot, they're putting a ton of spin on the ball because they get ridiculous racket head speed which allows them to have a margin for error even on relatively flat trajectory balls.
No one hits "flat" but some balls are flatter and Fed has the ability to hit numerous kinds of forehands including classic "flat" type strokes.