Rest before we start in battle? It’s a trap (6,3)
I believe the answer is:
spider web
'a trap' is the definition.
(spider web is a kind of trap)
'rest before we start in battle?' is the wordplay.
'rest' becomes 'spider' (I've seen this before**).
'before' is a charade indicator (letters next to each other).
'start in' indicates taking the first letters.
The initial letter of 'battle' is 'b'.
'spider'+'we'+'b'='SPIDER-WEB'
'it's' is the link.
(Other definitions for spider web that I've seen before include "Very fine trap" , "Insect trap" , "can catch bugs" , "weave" .)