Assists are Planetside's method for tracking Support Experience Points and how support character gain Merits. An assist is awarded after a player that you supported scores a kill. This is denoted on the HUD on the Session Stats Bar with an "A: ". Assists are also gained by operating a vehicle that has gunners or bombardiers that are making kills using your vehicles weaponry.
Support activities include healing, repairing, hacking, and other helpful activities. An assist timer will start after the first kill the person you supported makes. Any additional kills during this time will also count as assists. This timer is a minimum of 5 minutes and a maximum of 10 minutes, depending how much you supported the player. If the player dies, the tracker stops, unless he is revived. Locker Hack and hot drop assist timers start at the time of the assist, rather than after the first kill.
When a support-related assist is scored, a certain amount of the Battle Experience Points that the supported player scored for the kill is returned back to the supporter in what is called Support Experience Points. The amount of BEP returned to the supporter is dependent on how much you supported them, the more you supported them, the more SEP you receive. Note that "kills" on deployables and Wall Turrets will count as an assist on the HUD, but only player kills will count toward merits and give SEP.