Just seen this being done at the All England mens doubles...it's legal..I think..Something quite innovative from the Danes.
When the doubles sets up for serve and is holding the shuttle and racquet stationary (backhand serve), he then moves shuttle and racquet together with the arms making a motion similar to a window wiper. He then serves.
I think this motion to serve have been used in the past by doubles players. In this case, is there any advantage doing the serve this way? What is the effect it has on the shuttle trajectory say compared to one back/forward motion serve?