Global cricket tournaments schedule spare days for some fixtures and not for others, which produces recurring complaints whenever rain ruins a match without one. The allocation follows from cost rather than from principle.
A reserve day is an expensive commitment
Holding a day in reserve means keeping a stadium, its staff, security, broadcast crews and both squads available for a match that will usually not be played.
Those costs are incurred whether or not the day is used, and they scale with the number of fixtures given the protection.
Granting reserve days to every match in a large tournament would extend it by a week or more, which the international calendar cannot absorb.
Group matches can absorb a washout
A rained-off group fixture is usually shared as a tie, and each side takes a point, which keeps the table meaningful without replaying anything.
Because every team plays several group matches, one abandoned game rarely determines qualification on its own, though it can contribute to it.
The tournament therefore accepts the disruption, on the grounds that the competitive damage is spread rather than concentrated.
Knockout matches have no such cushion
A semi-final abandoned without a reserve day must be decided by a tiebreaker, usually group position, which eliminates a side that never had a chance to play.
That outcome is difficult to defend, since the entire tournament to that point exists to produce a contest that then does not happen.
Reserve days are consequently concentrated at the knockout stage, where the cost of an unplayed match is highest and the number of fixtures is smallest.
Shortened matches are the first remedy
Before a reserve day is used, officials reduce the number of overs to fit the available time, applying a revised target calculation to keep the match fair.
A match can be shortened substantially and still constitute a result, so the reserve day is a fallback rather than the primary response to weather.
Minimum-overs thresholds exist below which no result is possible, and it is only beneath that line that the spare day becomes relevant.
Venue selection does more work than reserve days
Tournament planners choose host cities and dates partly on rainfall patterns, which reduces the frequency of the problem before scheduling addresses it.
Drainage capacity is a criterion in venue selection too, because a ground that can restart play within an hour of heavy rain loses far fewer matches.
The reserve day protects the few fixtures where everything else has failed, which is why it looks arbitrary from outside and is largely economic from within.
