Dew, and why it decides more night matches than rain

There is a factor in limited-overs cricket that is larger than team selection, larger than the toss on most days, and completely invisible on a scorecard. Water condenses on the outfield after dark, and one of the two sides has to bowl in it.

What dew actually is

Air holds a certain amount of water vapour, and the amount falls as the air cools. After sunset the grass radiates heat, its surface drops below the dew point of the air just above it, and the water condenses out onto the outfield.

The three conditions that produce it are clear skies, still air and high humidity. That combination is common in a great deal of the cricketing world between about October and March, which is exactly when the international calendar schedules most of its evening limited-overs cricket.

Grounds vary enormously. A ground at altitude with a breeze may see none. A coastal ground in high humidity can be soaked by the twelfth over of the second innings, to the point where the ball is dried with a towel between deliveries.

What it does to the bowling

Three separate things, and they compound.

A wet ball will not grip. This is the one that matters most. A finger spinner's revolutions come from dragging the fingers across the seam, and a wet ball slides out of the hand. The stock delivery skids on straight, the ball does not dip, and a bowler who was the captain's wicket-taking option becomes somebody to be hit through the line.

A wet ball will not swing, and cannot be cut. The seamer loses conventional swing because the shiny side will not stay dry, and loses the cutter and the slower ball because both need finger pressure across a dry surface. What is left is the yorker, at pace, which is the hardest delivery in cricket to land repeatedly.

A wet ball is heavier and comes off the bat faster. Not by much, but enough to shorten the reaction time of a fielder inside the circle.

What it does to the fielding

A wet outfield behaves like a faster one. The ball skids across the top of the grass rather than sinking into it, which turns a comfortable two into a boundary and makes any misfield in the ring expensive.

Catching is worse in two directions. The ball is slippery, and the fielder's hands are wet. Sides that field second in heavy dew drop more catches than they would in the afternoon, and the drops come at the point in the innings when they are most expensive.

The subtler effect is on the fielders' movement. A wet outfield is slower underfoot for a sprinting fielder even while it is faster for the ball, which is the worst possible combination.

What it does to the toss

At a ground with reliable dew, the toss stops being a marginal advantage and becomes the largest single factor in the match.

Both captains know it. Both want to field first and bowl in the dry, then chase with a wet ball being bowled at them. One of them wins the toss and one does not, and the one who does not is now defending a total with an attack that has lost its two main weapons.

What grounds do about it

The countermeasures are real and only partly effective.

Chemical sprays applied to the outfield reduce surface tension so the water spreads rather than beading. They help and they wear off.

Rope dragging, where a heavy rope is pulled across the outfield between innings and during breaks, physically removes some of the water. It is used everywhere and it is a holding action rather than a solution.

Scheduling is the only genuine fix. An afternoon start that finishes before the dew point is reached removes the problem entirely, and it is the option that broadcasters will not accept because the audience is in the evening.

Where it does not happen

It is worth being clear that this is a conditional problem rather than a universal one, because the internet tends to invoke dew for every chase that succeeds.

Day matches have none of it. High-altitude grounds rarely see it, because the air holds less moisture to begin with. Windy grounds see less, because moving air does not sit still long enough to cool below the dew point. Dry-season matches in arid regions see almost none at all, however late they finish.

The grounds where it is close to guaranteed are humid, coastal or riverine, and playing in the cooler months. Anybody who has watched cricket at those venues can name them, and the captains certainly can, which is why the toss at those grounds is watched more closely than the first ten overs.

Why nothing adjusts for it

Rain has Duckworth-Lewis: a method, a table, and a revised target that both sides accept. Dew has nothing.

The reason is measurement. Rain is binary and observable — it is falling or it is not, and the overs lost are countable. Dew arrives gradually, varies across the outfield, and its effect depends on the attack, the pitch and the batters. There is no number to feed into a formula.

Proposals exist. Splitting each innings into two halves so both sides bat and bowl in both conditions has been tried in domestic competitions and is unpopular with everybody. Reversing the toss advantage is not a thing you can legislate.

How to spot it while watching

Four cues, in the order they appear.

The bowler drying the ball on a towel between deliveries. The clearest signal, and it usually starts around the tenth over of the second innings.

The spinner being taken off early. If a side's main spinner has bowled two overs and disappeared in a chase, the captain has concluded the ball will not grip.

Fielders wiping their hands on their trousers before every ball. Almost unconscious, and it happens constantly once the dew is down.

Boundaries from shots that were not middled. Edges running away for four through third man, and pushes into the covers reaching the rope, are the outfield telling you what the conditions are.

The short version

Dew is the largest unmeasured factor in white-ball cricket. It takes away the skills that limit a chase and gives nothing back, and the side that loses the toss at a dewy ground has already lost something the scorecard will never show.

If you want the other side of conditions, the toss and how much it is actually worth covers what a captain is really deciding, and Duckworth-Lewis covers the one condition cricket does adjust for.