Son exercises in part of play -- look! (6)
I believe the answer is:
aspect
'look' is the definition.
(I know that look can be written as aspect)
'son exercises in part of play' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'exercises' becomes 'pe' (Physical Education class).
'in' indicates putting letters inside.
'part of play' becomes 'act' (a play is made up of acts).
's'+'pe'='spe'
'spe' going inside 'act' is 'ASPECT'.
(Other definitions for aspect that I've seen before include "Face" , "Distant view of a wide area" , "Particular or distinct element, of a problem say" , "Vista, panorama" , "Prospect, view" .)