The most common and most likely answer to this crossword clue is the 9 letter word IRREGULAR
I've seen this crossword clue in Financial Times
I
R
R
E
G
U
L
A
R
More clues leading to the result IRREGULAR
- Disorderly Irish customer, a familiar one
- Against the rules, I run then pull back in behind
- Rough Irish customer, a frequent visitor
- Current Republicans holding a gun up for soldier
- Suspect guerrilla’s left to become resistance fighter
- Extraordinary rear girl jiggles around for all to see
- Not conforming to rules, one member of gang helping Sherlock?
- Unconventional air that’s missing A flat
- Kind of soldier, embracing left instead of right, turns into guerrilla
- Unofficial Irish king holding a gun up
Buddy explains!
The straight part
We know that "resistance fighter" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case resistance fighter = irregular.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does IRREGULAR mean?
IRREGULAR noun- A soldier who is not a member of an official military force and, often, does not follow regular army tactics
- One who does not regularly attend a venue
- Nonstandard; not conforming to rules or expectations
- (of a surface) rough
- Without symmetry, regularity, or uniformity
- (of a polygon) not regular; having sides that are not equal or angles that are not equal
- (of a polyhedron) whose faces are not all regular polygons (or are not equally inclined to each other)
- (grammar, of a word) not following the regular or expected patterns of inflection in a given language