At the drop of a hat

Origin

The phrase likely emerged in the 19th century, drawing its vivid imagery from a common method of signaling an immediate start or conclusion to various events. Picture the scene: a duelist's second dropping a hat to signal the commencement of a fight, an auctioneer dropping a hat to close a bid, or a starter dropping a hat to begin a race. This simple, instantaneous gesture provided a clear and unmistakable signal for immediate action, requiring no preparation or delay once the hat was released, thus perfectly capturing the essence of doing something without a moment's notice.