brutal, ferocious, savage, vicious, violent
armed
criminal
common (BrE,law)
aggravated (law), serious
felonious, felony, misdemeanor (all AmE,law)
alleged
attempted
indecent, physical, racial (esp. BrE), sexual
He was convicted of rape and another six counts of indecent assault.

domestic

series, wave

carry out (esp. BrE), commit
assaults committed by teenagers

be the victim of, suffer
report
He reported the assault to the police.

happen, occur, take place

assault against
Better street lighting has helped reduce the number of assaults against women.

assault on, assault upon

allegations of assault
allegations of police assault on the boy

assault and battery (law)

all-out, direct, frontal, full-scale, major, massive
After an all-out assault the town was captured by the enemy.

deadly, fierce
fresh, further
sustained
She used the article to make a sustained assault on her former political allies.

relentless
initial
final
successful
aerial, air, airborne, amphibious, ground
air assaults by fighter planes

military
terrorist
verbal
legal
a two-year legal assault on alleged tax fraud

series

begin, carry out, conduct, launch, lead, make, mount
Enemy troops launched an assault on the town.

launch into
He launched into a verbal assault on tabloid journalism.

come under, face
The factory came under assault from soldiers in the mountains.

survive, withstand
The garrison was built to withstand assaults.

course (BrE)
They took part in a vigorous army assault course.

operation
gun, rifle, weapon
force, team, troops
helicopter, ship, vehicle

under assault
Today these values are under assault.

assault on
a series of assaults on enemy targets