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 (2004), 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!"
The trivia items below may give away important plot points.
Henry Allen mentions in passing that his mother's maiden name was Garrick. This is a nod to John Wesley Shipp, the actor who plays Henry Allen, who also played The Flash in The Flash (1990), implying that he could have become a speedster in an alternate reality. This has sparked speculation that the man in the iron mask in Zoom's lair is in fact Earth-2 Henry Allen/Henry Garrick.
As lightning strikes his wand, Cisco directs it to S.T.A.R. Labs and yells "Great Scott! It's working!" This in reference to Back to the Future, where Dr. Emmett Brown uses a lightning strike to charge the DeLorean time machine and send Marty to 1985 from 1955.