Fig.: to begin doing something at full speed

Don't hit the ground running before you find the facts and understand what it is about

Non partire in quarta prima di aver capito di che cosa si tratta

He loves your new project and he's ready to hit the ground running to help you in any way he can

Gli piace da morire il tuo nuovo progetto, ed è pronto a partire in quarta per aiutarti come può

The runner took off at top speed trying to leave behind the strongest opponents right off the start

L'atleta è partito a tutta cercando di distanziare da subito gli avversari più ostici

The origin of this term is disputed. It may come from troops dropped into a combat zone, from stowaways jumping off a freight train as it nears the station, or from Pony Express riders avoiding delay when they changed mounts (Christine Ammer: The American Heritage dictionary of idioms)