Bullpen Roles and Leverage
Use the best reliever in the biggest spot, not only the 9th.
How it actually works. The modern structure gives one pitcher the ninth with a lead, another the eighth, and everyone else the innings that are left. Leverage measures how much a given moment can swing the outcome of the game, and it is often at its highest in the seventh with the bases loaded and the heart of the order up, not in the ninth with nobody on and the bottom of the order due.
Why it is done, and when it is wrong. Everyone in the game knows the best reliever should pitch the highest leverage inning, and almost nobody does it, which makes this one of the clearest examples of an incentive problem inside a sport. The save is a statistic that pays players in arbitration, roles give relievers routine, and a manager who uses his closer in the seventh and loses in the ninth is destroyed for it in a way he never is for losing conventionally. The result is a structure that is defensible for human reasons and slightly wrong on the merits.
What people get wrong about it. Postseason baseball is where this changes, and it is worth watching for. Roles evaporate in October because the incentive to protect a routine disappears, and it is the clearest evidence available that everyone knew all along.
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