a person who is involved in a small group that uses irregular tactics to fight with a larger and more organized group, especially as an act of rebellion;
e.g. The group sent one guerrilla to see if the gates were guarded.
(adjective)
unplanned or unconventional, and often somewhat extreme and/or aggressive in nature;
e.g. The company started using guerrilla tactics for advertising in order to reach as broad an audience as possible.