The phrase "active fighter" is correct and usable in written English.
It can be used to describe someone who is currently engaged in fighting, whether in a literal sense (such as in a sport or military context) or metaphorically (such as in a struggle for a cause).
Example: "As an active fighter for social justice, she dedicates her time to advocating for marginalized communities."
Alternatives: "current combatant" or "engaged fighter".
"Historical accounts describe him as an active fighter in battle, so he was clearly able to do strenuous physical activity.
Hopkins, who said this was his best performance, picked apart Pavlik in the early rounds, reducing the younger, typically more active fighter to a standing target.
Although Ibragimov was clearly the more active fighter in the early rounds, he could not get close enough to Klitschko to connect.
Every active fighter above 10st and below 12st has a plan to fight Mayweather, a desire based on the golden pot.
Román González, flyweight, 27 González, who some consider possibly the second best active fighter on the planet, is finally poised to appear on a big US network, HBO, in May.
It is my belief that the continuation of Jermain's career as an active fighter places him at unnecessary risk," then re-joined Taylor's team when he made a comeback.
Though Colombia's military is clearly a superior force, the FARC retains 8,000 active fighters and continues to disrupt economic activity.
The structure and size of America's armed forces ten army combat divisions, 11 aircraft carriers, 13 active fighter-aircraft wings—is justified on the assumption of its having to fight two conflicts on a scale similar to the 1991 war against Iraq at virtually the same time.
Mr. Ocalan's group is believed to have 4,500 active fighters.
Hezbollah has an extensive infrastructure, an estimated two to three thousand active fighters, and thousands of additional members.
While Saudi Arabia does not lack Qaeda sympathizers, the number of organizers and active fighters is unknown.
