(verb) To create hostility in others, causing them to attack you. This is frequently seen in MMOG's (massively-multiplayer online games) when a player draws the attention of one or more hostile NPC's (non-player characters) and is attacked by them. Also seen is the "chain agro", where the hostile NPC who was agroed causes the next nearest NPC to also agro on the player, setting up a chain reaction.
"Stay against the left wall to avoid agroing the goblins." "Look at that idiot, he just ran ahead and agroed the whole room."