Keep away from bore — don't get involved (5,4,5)
I believe the answer is:
leave well alone
'don't get involved' is the definition.
(I've seen this before)
'keep away from bore' is the wordplay.
I cannot quite understand how this works, but
'away' could be 'a' (abbreviation as used in sports fixtures) and 'a' is found in the answer.
'bore' could be 'well' (I've seen this before) and 'well' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for leave well alone that I've seen before include "Draw no water" , "fail to pick up at watering-hole?" , "Good job Tommy Stout didn't" , "Avoid interfering" , "make no waves" .)