bitter, fierce, hard, heavy, intense, serious
bloody
continued, continuing
fresh (esp. BrE), renewed
sporadic
constant
hand-to-hand
The sword and mace were the preferred weapons for hand-to-hand fighting.

house-to-house, street, urban
factional

end, halt, stop
The talks are intended to end the fighting.

take part in
The conspirators took no part in the fighting which ensued.

be killed in, die in
escape, flee
refugees fleeing the fighting

take place
begin, break out, erupt, flare, start
Fierce fighting broke out among the refugees.

ensue, follow
continue, go on
rage
For nearly two months the fighting raged.

intensify
die away, die down, diminish
Even if the fighting dies down, no answer is in sight to the political crisis.

cease, end, stop
resume

during the fighting, in the fighting
He was badly wounded during the fighting.

fighting between
There has been renewed fighting between the government forces and the rebels.

do the/sb's fighting
He prefers others to do the fighting for him.

a lull in the fighting

Fighting is used with these adjectives:
fit