Start of play in which cow gets away (5,3)
I believe the answer is:
bully off
'start of play' is the definition.
(I've seen this before)
'cow gets away' is the wordplay.
'cow' becomes 'bully' (both can mean to intimidate someone).
'gets' is a charade indicator (letters next to each other).
'away' becomes 'off' (synonyms).
'bully'+'off'='BULLY-OFF'
'in which' acts as a link.
(Other definitions for bully off that I've seen before include "start play again" , "(Re-)start hockey game" .)