Suddenly turn west, interrupting start of rally? (6)
I believe the answer is:
swerve
'start of rally?' is the definition.
'swerve' can be an answer for 'start' (thesaurus). I'm unsure of the 'of rally?' bit.
'suddenly turn west interrupting' is the wordplay.
'suddenly turn' becomes 'serve' (I can't explain this - if you can you should give a lot more credence to this answer).
'west' becomes 'W' (abbreviation).
'interrupting' is an insertion indicator.
'serve' placed around 'w' is 'SWERVE'.
Can you help me to learn more?
(Other definitions for swerve that I've seen before include "Using spin" , "Move aside quickly" , "Sharp turn" , "Turn aside from straight course to avoid something (6)" , "Suddenly move off course" .)