jump the gun

Idioms  

1. 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]

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Example Sentences

Okay, I do want to jump the gun because I’m certain of what we’re seeing.

From Washington Post

But the curators of classic popular culture love to jump the gun on anniversaries — especially when the artifact in question is the most beloved movie of all time.

From Time