Prisoner's Dilemma strategies
Always Defect
Defect on every move, whatever the opponent does.
Played by Blackmoor United
Where it comes from
The single-round rational play, and the reason the Prisoner's Dilemma is a dilemma at all. In one shot it is unbeatable. Repeated, it is a different question.
How it plays
Always Defect is correct and it is a trap, and holding both of those at once is the whole point of the Prisoner's Dilemma. In a single round, defecting is the dominant move against any opponent: whatever they do, you do better by defecting. A game theorist will tell you that without hesitating and they are right.
Iterate the game and the answer changes, because your opponent is now able to respond to what you did last time. Against a field of reciprocators, permanent defection buys you a series of mutual punishments, which is a poor score repeated fifty times. Axelrod's tournaments were won by nice strategies, and Always Defect finished a long way from the top in both.
It has never been harmless, and this is the part people skip. Always Defect eats the naive. Any strategy that will not answer back is a maximum pay-off every single round, so a league containing enough soft sides is a league in which relentless aggression prospers. Where it fails is against anyone who returns it.
In football it is total, permanent pressing, every duel, no exceptions. It is overwhelming against a side that will not answer and it produces a grinding, chanceless mess against a side that will. The interesting question is never whether it is nasty; it is what fraction of the league it is allowed to feed on.
In this league
Blackmoor United of Blackmoor play Always Defect. That the ruthless side always eats, and someone else can worry about how. They have not played yet this season.