Vision certainly possessed by rowing squad (8)
I believe the answer is:
eyesight
'vision' is the definition.
(eyesight is your vision)
'certainly possessed by rowing squad' is the wordplay.
'certainly' becomes 'yes' (both can be used to answer in the affirmative).
'possessed by' means one lot of letters goes inside another.
'rowing squad' becomes 'eight' (crew of eight rowers).
'yes' going within 'eight' is 'EYESIGHT'.
(Other definitions for eyesight that I've seen before include "Showing sense" , "Power of vision" , "Yes, eight required for vision" , "perception" , "Seeing faculty" .)