If you are under starter's orders it means you are waiting for a signal to start a race.
The athletes have been waiting for this moment for years. They’re under starter’s orders. And they’re off!
It was only a second or two but the runners seemed to be under starter’s orders for hours before the pistol was fired.
Don't confuse it with
Under arms means supplied with weapons and prepared to start fighting
The rebels were under arms and an attack was just a matter of time.
204 nations will be taking part in the London 2012 Olympics with about 10,500 athletes participating in the competition. There will be 302 events in 26 different sports. This is the third time London has hosted the games. The first time was 1908 and the second in 1948.