Scout is when your main job is running around at more than 100kph armed with ECM and/or BAP spotting targets for the main team. Your defining trait is speed.
Harrasser is when your main job is rushing quickly into where a group of enemies are ahead of the main force in order to strafe through the enemies with all your weapons and then disappear only to reappear again after your main force hits or to distract the enemy by flanking them from behind and then disappearing. You also frequently act as a lure for the main force to attract enemies into your team's ambush. Your defining trait is building your mech around more speed than firepower.
Skirmisher is when you fight with the main force but fight consistently at a fast speed, being able to get in and out of a fight quickly, typically packing more firepower than a harrasser but never fully engaged with a single enemy in an all out brawl. Your defining trait is trying to get as much firepower as possible at a reasonably high speed. You also try to build around having higher alpha rather than higher DPS as you don't stick in a fight long enough for DPS to be meaningful and you have plenty of running around time to cool down before strafing back in for another alpha.
Brawler is when you stick into a fight and typically slug it out focusing on a single enemy. Your defining trait is lots of armor and firepower. You also focus on higher DPS rather than higher alpha when designing your build in order to maintain a high sustained damage on your engaged target.
Support is when you sit back behind friendly lines and rain tons of LRM or long range fire at the enemies that are engaged with your brawlers. Your defining trait is packing as much long range ammo or weapons with sacrifice on the part of speed.
Edited by Pr8Dator, 28 December 2012 - 07:22 AM.