Start of invasion deployed sniper fire (7)
I believe the answer is:
inspire
'fire' is the definition.
(I know that inspire is a type of encourage)
'start of invasion deployed sniper' is the wordplay.
'start of' says to take the initial letters.
'deployed' indicates an anagram.
The first letter of 'invasion' is 'i'.
'sniper' with letters rearranged gives 'nspire'.
'i'+'nspire'='INSPIRE'
(Other definitions for inspire that I've seen before include "Stimulate person to adventurous thought or deed" , "Galvanize" , "Animate (with feeling)" , "move!" , "Breathe in and infuse into the mind" .)