Uncompromising approach that leads to things piling up (9,6)
I believe the answer is:
collision course
'uncompromising approach' is the definition.
'collision course' can be an answer for 'approach' (I have seen 'Dangerous approach' mean 'collision course' so perhaps 'approach' could also mean 'collision course'). I'm unsure of the 'uncompromising' bit.
'leads to things piling up' is the wordplay.
I cannot really understand how this works, but
'up' could be 'is' (I've seen this in other clues) and 'is' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'that' is the link.
Can you help me to learn more?
(Other definitions for collision course that I've seen before include "what looks like leading to conflict" , "Dangerous approach" , "leads to certain conflict" , "opposing philosophies leading to conflict" .)