A goal after the 80th minute in the derby?
How it resolves
Any goal from the 81st minute onwards counts, stoppage time included, and if nobody scores that late it’s a No.
What we'd look at
We'd bet more people underprice this than overprice it, since late goals are common once legs get tired and one side's chasing the game. Still, we'd check how many of each team's goals this season came after 80 minutes (it varies a lot between teams) before we trusted the price. A team that's conceded a lot late on tends to keep doing it, at least in our experience.
About practice markets
The price here is simulated, which means nobody's on the other side and nothing you do will move it. We built it that way on purpose, because the habit we want you to pick up is checking a price against your own number before you trade, and that's far easier to practise when a mistake costs you nothing. Try putting in a probability that's a few points away from the price and watch what happens to the expected value and the Kelly stake (that's the whole course in miniature).