We measured projected rotational velocities of more than a hundred apparently single sdBs .
A comparison is made with sdB stars in binary systems with orbits so wide , that tidal interaction becomes negligible .
All of these stars are slow rotators ( v _ { rot } \sin { i } < 10 { km s ^ { -1 } } ) with EC 22081 - 1916 being the only exception .
This single star has the highest projected rotational velocity ever measured for an sdB ( v _ { rot } \sin { i } = 163 { km s ^ { -1 } } ) and might have been formed by a merger event .
The merger of a red-giant core and a low-mass , main-sequence star or substellar object during a common envelope phase fits particularly well with observations .
The implications of our results for hot subdwarf formation are briefly discussed .