New alert in court battle (8)
I believe the answer is:
waterloo
'battle' is the definition.
(1815 battle)
'new alert in court' is the wordplay.
'new' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'court' becomes 'woo' (both can mean to romance someone).
'alert' with letters rearranged gives 'aterl'.
'aterl' inserted into 'woo' is 'WATERLOO'.
(Other definitions for waterloo that I've seen before include "Wellington's victory" , "Battle - station" , "Decisive battle" , "song" , "Losers may meet theirs" .)