The Laws of Cricket say you can declare in any game. In practice, most limited overs competitions ban declarations and its rare that declaring would bring a benefit in such a game.
As a quick reminder, almost all cricket falls into two categories:
- A limited over game (such as a one-day 50-over or a T20) has a maximum number of overs for each innings (even if the team is not dismissed) and does not allow for a draw (but games can be tied.)
- Other games (such as a Test match or other first class match) have a time limit on the entire game but not on each innings; can only be won if the losing side has completed all of its innings (usually two); and can end in a draw if nobody has won when the time limit expires.
The Laws of Cricket say a team can declare its innings over at any time, or forfeit an innings (in effect, declaring before the innings even starts.) This makes sense in a first class match when a team has a big lead and is concerned that if it carries on with its innings, it may not leave enough time to dismiss the other team and win the game.
In a limited overs match, this usually makes less sense. Declaring your innings won’t affect the number of overs in the opponent’s innings and there’s no risk of a draw anyway. Declaring could increase the chances of completing the game if rain is expected, but this isn’t as much of a factor with systems such as DLS available.
Perhaps the only situation a declaration makes sense in a limited overs game is if a team is desperate to win and want to make sure the opponents have enough overs that a result under DLS is allowed, rather than the game being abandoned and nobody winning. (There’s often a rule that says both sides must bat a certain number of overs such as five in T20 or 10 in a one-day game before DLS can be used to decide a winner.)
The most notorious declaration in a one-day game came in very specific circumstances. In 1979, Somerset declared after just one over (having scored one run) in a one day game against Worcestershire. Although Worcestershire easily won the game (scoring the necessary two runs in just ten balls), they were still eliminated from the tournament (the Benson & Hedges Cup).
This was because the league table before the game meant Worcestershire could only advance to the knockout stage at Somerset’s expense if they not only won the game, but significantly improved their overall strike rate in the competition. This was an earlier version of net run rate, used to separate teams that are level on points in a group stage. Somerset’s declaration meant it was mathematically impossible for Worcestershire to improve their strike rate by enough to overtake Somerset in the group table.
The declaration was incredibly controversial and led to Somerset being thrown out of the competition, with critics saying they had followed the letter of the law but not the spirit of cricket. This led to organizers banning declarations in future games, something that is now common in the playing conditions for limited overs competitions. These are additional rules that work alongside (and occasionally take precedence over) the general Laws of Cricket.
There is a less common format known as a one-day declaration game. This is where the total number of overs in the game has a limit, but the length of each side’s innings is not fixed. This means the team batting first can declare. This format is more like a first class match than a limited overs match because a draw is possible.