Side-track to avoid the start of trouble (5)
I believe the answer is:
shunt
'side' is the definition.
(thesaurus)
'avoid the start of trouble' is the wordplay.
'avoid' becomes 'shun' (shunning is a kind of avoiding).
'the start of' suggests taking the first letters.
The initial letter of 'trouble' is 't'.
'shun'+'t'='SHUNT'
'track to' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for shunt that I've seen before include "Motor collision" , "Rear end collision" , "Divert into alternative course, like train" , "Sidetrack" , "Arrange wagons; minor accident" .)