Vision certainly possessed by rowing crew (8)
I believe the answer is:
eyesight
'vision' is the definition.
(eyesight is a kind of vision)
'certainly possessed by rowing crew' is the wordplay.
'certainly' becomes 'yes' (both can be used to answer in the affirmative).
'possessed by' indicates putting letters inside.
'rowing crew' becomes 'eight' (a crew of eight rowers is called an 'eight').
'yes' inserted within 'eight' is 'EYESIGHT'.
(Other definitions for eyesight that I've seen before include "What's needed to see" , "Seeing ability" , "Power of vision" , "Visual faculty" , "Purpose of certain organs" .)