Does exercises and runs classes (8)
I believe the answer is:
performs
'does' is the definition.
('perform' can be a synonym of 'do')
'exercises and runs classes' is the wordplay.
'exercises' becomes 'pe' (Physical Education).
'and' means one lot of letters go next to another.
'runs' becomes 'r' (cricket abbreviation).
'classes' becomes 'forms' ('form' can be a synonym of 'class').
'pe'+'r'+'forms'='PERFORMS'
(Other definitions for performs that I've seen before include "Carries out, accomplishes" , "Carries into effect or functions" , "Acts as in play" , "Acts or executes" , "Carries out, acts" .)