At The Drop Of A Hat
De Volón Pin-Pon
To begin something at an indicated moment (the dropping of a hat), to star something without any delay.
Since long time ago, there have been many ways to indicate that a certain event had to start, especially competitions. They were started by different means, for example a whistle, the shooting of a gun, dropping a handkerchief or a hat, as the expression suggests. To drop the hat represents the signal that competitors need in order to get a of a competition started. This use has been now extended to any event that we start enthusiastically at a given signal.