Cook some grouse badly (5)
I believe the answer is:
grill
'cook' is the definition.
(grilling is a form of cooking)
'some grouse badly' is the wordplay.
'some grouse' becomes 'gr' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'badly' becomes 'i'll' (eg in ill-advised).
'gr'+'ill'='GRILL'
Can you help me to learn more?
(Other definitions for grill that I've seen before include "pump" , "quiz?" , "Grating" , "Cook under a flame" , "Cook under direct heat" .)