Cisco controls the Flash hologram to stop the getaway car. Just as he sends the hologram into a lightning spin to blind the driver, he yells "Leeroy!" Yelling Leeroy refers to a user created video from World of Warcraft (2005), where Leeroy Jenkins, not hearing the plan, charges in bellowing his own name and ends up getting his party killed.
There are a couple references to Harry Potter in this episode. 1st when Wells is telling Cisco to get his wand to use for the lightning. Cisco asks if it's the one he made for Mardon? Wells says, "No, the one you made for the Harry Potter convention last year." Then when Cisco is on the roof and about to use it he yells out a Potterworld spell, "Expecto Patronum!"