With your analogy, I would absolutely be warming up for an 800m sprint with about 400m of running. Not sprinting, no. But a combination of jogging and stretching. I'm no physio, granted, but only jumping up and down on the spot and stretching before sprinting for 800 metres could be risky for sustaining an injury. I've done exactly that before (Achilles). These are professional athletes trained to be fit for more than 80 minutes of play. Their 30 minutes of warming up isn't nearly at the same rigour as it will be in the game, and they're doing drills to minimise risk of injury during the game.