Exercise machine rated badly by philosopher (9)
I believe the answer is:
treadmill
'exercise machine' is the definition.
(I've seen this before)
'rated badly by philosopher' is the wordplay.
'badly' indicates anagramming the letters (letters in the wrong order).
'by' says to put letters next to each other.
'philosopher' becomes 'mill' (John Stuart Mill).
'rated' anagrammed gives 'tread'.
'tread'+'mill'='TREADMILL'
(Other definitions for treadmill that I've seen before include "Dreary round" , "Piece of gym equipment" , "Form of torture" , "Routine activity" , "Boring routine; old rotary device" .)