jump the gun = do things ahead of authorization jump the gun To start doing something too soon. http://www.thefreedictionary.com/jump+the+gun

"to jump the gun" means to do something too soon, especially without thinking carefully about it If someone running in a race jumps the gun, they start running before the gun has been fired to start the race. Example: He started to play the violin before the conductor pointed at him, but later he apologized to the rest of the violinists for jumping the gun.

Think of a race with 10 people. One person starts running before the "go" is said. The person jump the gun. So it is like going before your suppose to go, a false start.

To do something urgent.