Originally Posted by WildVolley
I once watched Karlovic play on court 6 and I had a seat right at the top of the backstop. We almost got pegged by a few high bouncing down the line serves. That guy is the most impressive server I've ever seen even though it seems like he hardly swings at the ball.
Very good observation. He doesn't look like he is putting any effort. He also contacts in the sweetspot, not at the tip, in most cases. I think his height and arm length give him a lever-arm effect on the speed of the ball which no one else can get. He also does something with his fingers (like readjustment) at the end of the back swing.