jump the gun
ACT PREMATURELY, act too soon, be over hasty, be precipitate, be ahead of oneself

[TahlilGaran] Dictionary of Contemporary English ▲

jump the gun
to do something before it should be done.
We do not want to jump the gun by making a statement about what caused the explosion before the investigation is completed.

Etymology: based on the literal meaning of jump the gun (= to begin to run a race before the gun that signals the start has been shot)

[TahlilGaran] English Idioms Dictionary ▲

jump the gun
start before the starting signal or before you should start (as in a race)
My friend jumped the gun and applied for the job before applications were being accepted.

He jumped the gun and started selling the tickets before he should have.

[TahlilGaran] English Idioms Dictionary ▲

jump the gun
v. phr.
1. To start before the starter's gun in a race.
The runners were called back because one of them jumped the gun.
2. informal To start before you should; start before anyone else.
The new students were not supposed to come before noon, but one boy jumped the gun and came to school at eight in the morning.
The students planned to say happy birthday to the principal when the teacher raised her hand, but Sarah jumped the gun and said it when he came into the room.

[TahlilGaran] English Idioms Dictionary ▲