The Ashes opener, conditions and the toss
In some conditions the coin is worth more than either team's recent form. Here is how to work out roughly how much, before it is flipped.
Before either side is assessed, the first question about a Test match is how much the coin is worth at this ground in these conditions. At some venues the honest answer is almost nothing. At others it is larger than the gap between the two teams.
What makes it matter
Two mechanisms. The first is deterioration: a pitch that turns and bounces unevenly by day four makes the fourth innings the hardest place to bat, and the side batting last is decided by the toss. The second is the first morning, where overcast conditions and a new ball can produce an hour that decides the match.
The two point in opposite directions, which is why the toss is not simply "bat first". A captain facing a green surface under cloud may prefer to bowl, and the same captain on a dry surface will bat without thinking about it.
Pricing it before it happens
If winning the toss is worth six points of match probability and it is a fair coin, then a pre-toss price should sit at the average of the two post-toss prices. It usually does, because books are not naive about this.
Where it goes wrong is when the conditions are unusual and the venue's history is being applied mechanically. This is the same failure as applying league averages to a specific fixture: the ground's long-run toss value is not this week's toss value if the preparation has been different.
What we are watching
The forecast, which is genuinely predictive here in a way it is not in most sports, and the amount of grass left on the surface at the final inspection. Both are observable before the price stops moving.
What this does not tell you
Any specific number for what the toss is worth. Estimates from historical records confound the toss with the quality of the sides who won it, and separating the two properly needs more Test matches than have been played at most grounds.
Common questions
How much is winning the toss worth in Test cricket?
It varies enormously by venue and conditions. At some grounds it is close to worthless; at others, on a pitch expected to deteriorate, it is worth several percentage points of match probability.
Can you bet before the toss?
Yes, and the price will move once it is decided. Betting before is a bet on the coin as well as on the cricket.
What conditions make the toss most valuable?
A pitch that breaks up, giving the fourth innings side a much harder task, or overhead conditions that assist swing on the first morning.