Fall upon a line of approach, verbally (6)
I believe the answer is:
attack
This clue is a triple definition!
'fall upon' is the first definition.
(thesaurus)
'a line' is the second definition.
(thesaurus)
'of' is a link.
'approach verbally' is the third definition.
'attack' can be an answer for 'approach' (thesaurus). I'm unsure of the 'verbally' bit.
Can you help me to learn more?
(Other definitions for attack that I've seen before include "Set upon" , "Launch an offensive" , "Hit out" , "Offensive or inslaught" , "Pitch into" .)