Communist crossword compiler's dog? (3,6)
I believe the answer is:
red setter
'dog?' is the definition.
(red setter is a kind of dog)
'communist crossword compiler's' is the wordplay.
'communist' becomes 'red' (red can informally mean communist).
'crossword compiler' becomes 'setter' (someone who sets crosswords).
'red'+'setter'='RED SETTER'
(Other definitions for red setter that I've seen before include "Breed of dog" , "Gun dog" , "Shepherds are delighted to see this" , "description of evening sun?" , "My best friend" .)