The reason everyone goes Runaan ' s on Caitlyn is because she builds charges off the Runaan ' s onhit effects when they cleave to 2 adjacent targets , so rather than getting 1 charge per auto she potentially gains 3 . Now , with that said a big consideration that is missing in this case is that it assumes the enemy kill target is standing in the middle of their tanksbacklineminion wave . If not , then the Runaan ' s headshot charges don ' t apply in which case the faster IE rush should I suspect ! outweigh the Runaan ' s rush , because the benefit of doing so is conditional on something which isn ' t always occurring . Example Enemy Vayne engages on your Cait in lane , coming in at an angle where she is neither adjacent to her minion wave or her support ex . river side then Cait ' s Runaan ' s rush is totally useless , but an IE would fuck that Vayne up .