Skirmisher
/ˈskɜːrmɪʃər/
Definition 1 of 2
Pro Tip 1/3Warfare Role
The term 'skirmisher' implies a tactical role on the battlefield, not a rank or position. 
The general deployed his skirmishers to disrupt the enemy's advance.
Pro Tip 2/3Not Main Force
'Skirmisher' suggests a soldier not part of the larger army group but acting ahead or on the flanks. 
Skirmishers operated on the edges of the battlefield, unseen by the bulk of the troops.
Pro Tip 3/3Harassment Tactic
Skirmishers are known for harassing the enemy, creating confusion without direct combat. 
Using their speed, the skirmishers were able to harass the enemy's supply lines.