The act of acting in a way as to make yourself seem like a bigger threat than the rest of your squad, particularly in competitive team sports or MMORPGs. As a result, all or most of the opposition will immediately target the Puller. This is a popular tactic for hired Tanks so that their clients, who are usually weaker, will not be targeted by enemies potentially stronger than they wish to challenge. The client gets experience while the Tank usually gets money, items or other favors in return, partially as compensation for any damage taken or insurance for items lost upon defeat.
Oh crap! That sniper's got a bead on my location! I'm pinned down! Hey Grenadier, start pulling aggro for me so I can move!
Hold on a second, let me start pulling aggro for you so you can get some free shots off. Give me some medkits.