When a person, either real or fictional, turns their baseball cap through 180 degrees so that the peak faces backwards to physically represent that they have switched into "go-time" mode.
In episode 243 of Pokémon, Ash ketchum is challenged to a battle by long time rival Gary Oak. In acceptance of the challenge, Ash "Southbilled" by rotating his baseball cap 180 degrees suggesting that it was "go-time."
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