### Clue: Irregular ultimately out fighting to install Left? (9)
### Answer: GUERRILLA 
 ### Explanation: Definition: Irregular
 **Anagram of**(… fighting) [ "Irregular" **minus ****its last letter**(ultimately out)] **containing**(to install) L(abbrev. for "left").
Defn: … soldier/fighter.
A WIWD (wordplay intertwined with definition) clue.