Possible Clues:

• Irregular soldier sounds like big thug
• ____ warfare is named from its use in the Peninsular War
• What’s irregular or oddly regular about one line?
• Irregular soldier
• Irregular combatant
• Fighter disguised as real girl in uniform? On the contrary
• The Italian will disrupt flying, regular and irregular
• I left mutinous regular outside for one underground?
• Slip up badly in summer month, backing freedom fighter
• Irregular and liberal — mostly irregular and liberal