1
general::
Defend against, drive back, as in I've been fighting off a cold all week. This figurative use of the term, originally meaning "to repel an enemy" dates from the early 1800s.
American Heritage Idioms
2
general::
Phrase(s): fight someone or something off
to repel an attack from someone or something. • We fought the enemy attack off, but they returned almost immediately. • She fought off the mosquitoes all evening. • Jed fought the attacker off.
McGrawhill's American Idioms And Phrasal Verbs