jump the gun

jump the gun idiom
Start doing something too soon, act too hastily. For example, The local weather bureau jumped the gun on predicting a storm; it didn't happen for another two days. This expression alludes to starting a race before the starter's gun has gone off, and supplants the earlier beat the pistol, which dates from about 1900. [Mid-1900s]

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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