The Fight check is a type of Skill check typically prompted via encounter cards. It represents a test of the Investigator's physical performance in the scenario presented in the encounter.
A Fight check uses the value of the Investigator's Fight skill, plus any adjustments that the Investigator would receive from skill cards, allies, and Mythos card effects, plus any adjustment specified by this specific check. Unless otherwise specified, a single success is enough to pass the check.
A Fight check may also be used to close or seal gates.