The fastest recorded tennis serve, hit by Australian tennis player Sam Groth at the 2012 Busan Open Challenger in South Korea, rocketed down the court at 163.4 mph (263 kph). Groth, 24, who was ranked 340th in the world at the time, ended up losing the second-round match to opponent Uladzimir Ignatik from Belarus, who was able to return Groth's lightning-fast serve.
Groth's serve was so speedy that it increased the world record for fastest tennis serve by a whopping 5.3 percent. The previous fast-serve title was set in 2011 by Croatian player Ivo Karlovic, at 156 mph (251 kph).
Some caveats here: The Association of Tennis Professionals doesn't officially recognize speed records because of a lack of consistency in monitoring equipment. Still, the governing body of tennis confirmed that the radar gun at the Busan event was working and that other data collected at the event appeared to be accurate.
Tennis is one of the fastest sports on the world — for comparison, the fastest slap shot in hockey was just 106.6 mph (172 kph), and the fastest pitch in baseball was a mere 100.9 mph (162 kph). Both male and female tennis players regularly hit serves clocked at over 120 mph (193 kph).
So what makes a fast tennis serve? Some researchers have crunched the numbers and found that taller players tend to hit faster serves, according to Planet-Science.com. In part, long arms and legs may let players swing up to and through the ball, letting them generate greater racket-head speed.
But height can also help in a second way. The higher in the air a racket meets the ball, the more a tennis player hits down into the court, which effectively makes the court a bit bigger. Height adds a better angle and gives a player a greater margin of error. For the record, Groth is 6 feet 4 inches (1.9 meters) tall.