Sarah to go forth on the offensive (5)
I believe the answer is:
sally
This clue is a triple definition!
'sarah' is the first definition.
(Sally is a common pet form of Sarah)
'to go forth' is the second definition.
(thesaurus)
'on' acts as a link.
'the offensive' is the third definition.
(thesaurus)
(Other definitions for sally that I've seen before include "Set out - girl's name" , "- - Lunn, flat cake" , "army" , "A sortie or witty remark" , "Sortie; witty retort" .)