Following on

In cricket, a follow-on is where the team that bats second is forced to take its second batting innings immediately after its first, because the team was not able to get close enough to the score achieved by the first team batting in the first innings. If the second team to bat scores substantially fewer runs than the first team, the first team have the option of enforcing the follow-on, that is, instructing the second team to bat again immediately. In this case the sequence of batting innings will be first team, second team, second team and then, if required, the first team again. This is in contrast to the normal progression of batting innings which is first team, second team, first team, second team. The first team may choose not to enforce the follow-on, and bat themselves instead.

The rules governing the circumstances in which the follow-on may be enforced are found in Law 13 of the Laws of Cricket.

The number of runs by which a team must lead to enforce the follow-on upon its opponent is determined by Law 13 of the Laws of cricket, which takes the length of the match into consideration:

Where a match is shortened, the leads required to have the option of enforcing the follow-on are determined by how many days' (or part-days') play remain when the match starts. For example, suppose a match is scheduled for five days, but the first day is washed out because of rain. If the match then begins on the second scheduled day of the match, the team batting first needs a first innings lead of 150 runs or more to have the option of enforcing the follow-on. This only applies to time lost before the first ball has been bowled: if a five-day match starts on the scheduled first day but, say, the second day is completely lost, it still counts as a five-day match for the purposes of calculating the follow-on target.

The follow-on is not automatic; the captain of the leading team decides whether to enforce it. This is a tactical decision which the captain makes based on the state of the game, the conditions of weather and pitch, the apparent strength of the two sides, and the time remaining.

Conventional theory argues that the follow-on is almost always enforced. In his classic text The Art of Captaincy, Mike Brearley deals with the issue in a single paragraph and finds the advantages of doing so overwhelming. Certainly there are strong reasons for enforcing the follow on. The main reason is one of time. In two innings games, for a team batting first to win, it usually needs to dismiss the opposition twice. If it fails to do so, the game will end in a draw. Indeed it is a common tactic for a side which appears to be well-beaten to bat cautiously in its second innings and use up the remaining time so that the game does end this way. Enforcing the follow-on means that the trailing side takes its second innings earlier in the game and will therefore find it much harder to play for a draw by using up time. Another reason for enforcing the follow-on is the positive effect it can have on a team's morale, and the equal negative effect on that of the other.

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Wikipedia