Before the bats started swinging, the Iowa Cubs and Round Rock Express were moving to the groove before their game on Tuesday at Principal Park. During pregame, just a minute or two before the first pitch, the song, "Let's Get Loud," by Jennifer Lopez started playing. That's when Iowa Cubs pitcher Randy Rosario started doing the now-iconic arm dance by the "Backpack Kid," who first appeared with Katy Perry on Saturday Night Live. Express starting pitcher David Ledbetter responded by showing off his moves and adding some flare with an arm wave. The two men continued to twist and turn back and forth, even adding a Michael Jackson signature move.