In Infrared terms, a partisan is a political actor with real political difference with the hegemony. There is a difference between some belief or stated position and actual political position. Therefore it is possible for someone to hold left-wing views while their actual politics supports hegemony. For example, the CPUSA claims to be revolutionary, but their real politics consists of rallying leftists to vote for the Democratic Party. In contrast, a partisan has a position that is actually counter-hegemonic.
Infrared’s view of the partisan is heavily influenced by Carl Schmitt’s Theory of the Partisan.