The follow on

In a two innings match, if the side batting second scores substantially fewer runs than the side batting first, the side that batted first can force their opponents to bat again immediately. The side that enforced the followon risks not getting to bat again and thus the chance of winning. For a game of five or more days, the side batting first must be at least 200 runs ahead to enforce the followon; for a three or fourday game, 150 runs; for a twoday game, 100 runs; for a oneday game, 75 runs. The length of the game is determined by the number of scheduled days play left when the game actually begins.