shot clock

noun3

1. •
   A timer measuring the length of time since the last shot.
2. •
   A countdown of the time remaining within which the current server must serve the ball.

   • Top tennis stars will come under a 25-second shot clock in grand slam tournaments starting at the Australian Open in January. — 2017
3. •
   A counter of the total shots on net for a team in a game; or average shots on net per unit time for a game.