In a stern position, one over the eight? (3)
I believe the answer is:
cox
'one over the eight?' is the definition.
(a cox directs a rowing crew or 'eight')
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for cox that I've seen before include "Member of rowing crew" , "He's in charge of a racing boat and its rowers" , "Helmsman" , "Passenger vehicle" , "Boat's steerer" .)