Crude comment is what marks the end of court (8)
I believe the answer is:
baseline
'end of court' is the definition.
The answer and definition can be both locations as well as being singular nouns.
Maybe there's an association between them I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for baseline that I've seen before include "yardstick" , "Marks limit of play on tennis court" , "Starting point" , "Back of tennis court - standard" , "Out beyond this" .)