Accusation of assault (6)
I believe the answer is:
charge
I believe this clue is a double definition.
'accusation' is the first definition.
(thesaurus)
'assault' is the second definition.
(charging is a kind of assaulting)
'of' is the link.
(Other definitions for charge that I've seen before include "responsibility" , "Accusation (in court)" , "What a battery holds" , "person in custody" , "Legal accusation" .)