From http://english.people.com.cn/200505/14/eng20050514_184991.html Chinese Fu clocks fastest smash at Sudirman Cup Chinese doubles star Fu Haifeng has clocked the fastest smash ever with a racket in the ongoing badminton Sudirman Cup here, according to International Badminton Federation. IBF is conducting speed trials for the first time at one of its major events, with microwave sensors recording the speed of smashes on the main TV court (court 4) during this ninth edition of the World Mixed Team Championships. Fu has clocked the fastest smash of 332 kph so far, while Denmark's Kenneth Jonassen has recorded the fastest smash for a singles player at 298 kph (185 mph). IBF said in a statement on its official website that badminton could firmly stake its claim to be the world's fastest racket sport with the record. With women's singles shuttler Huang Sui hitting at 257 kph (160 mph), tennis star Andy Roddick's world-record serve of 246 kph (153 mph) is some way off of badminton's blistering pace. According to the statement, the speed-testing equipment is currently only able to record speeds of up to around 350 kph (217 mph), so the star shuttlers are already pushing the limits. The fastest recorded smash in badminton previously came from England's Simon Archer at 260 kph (162 mph).
But badminton also does decelerate much faster then other racket sport as well so clocking the fastest inital speed isn't really the most objective refrence i would like to see, i would be more interested at the speed when the bird crosses the net
still at that blistering speed it will make up for the extream deceleration. you have to bear in mind that a tennis ball travel much slower, and even slower once it touched the ground