They might draw the line at this in Stockley Park (7)
I believe the answer is:
offside
'this in stockley park' is the definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I can't see?
'they might draw the line' is the wordplay.
I cannot quite understand how this works, but
'line' could be 'side' (side is a kind of line) and 'side' is present in the answer.
The remaining letters 'off' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'at' acts as a link.
Can you help me to learn more?
(Other definitions for offside that I've seen before include "Illegally ahead of the ball in soccer" , "Foul position in soccer" , "(In a ball game) illegally positioned" , "Illegal football position between the ball and opponents' goal" , "(in the UK) a vehicle's right" .)