I remember shooting high school football when I was in high school in the late 1970s. I used black & white 400 ASA (now called ISO) film, and push processed it to 1600. It had grain like boulders. It wasn't butter smooth, but I got the shots.
You can essentially do the same now with digital. If you push your ISO high enough, you'll be able to stop the action. You might get more noise than is ideal, but you'll get the shot. You can try to eliminate some of the noise in post-processing. If you shoot in RAW, you'll be able to recover more info from the shadow areas in post-processing.
Today's football fields are pretty well lit at night. If you push your ISO to 1600, and shoot at f/2.8, you should be able to get a fast enough shutter speed to stop most action.
If the field is reasonably evenly lit, set your meter manually and leave it alone. If you let your camera auto-meter, it will have a tendency to blow out highlights. That is because much of the field and the background is often dark, especially if you are shooting from ground level. Remember, your meter is seeking an overall medium light level. This will throw off the meter and overexpose the players. Do some test shots early, and concentrate on getting proper exposure on the players, and don't worry if most of the background goes too dark. Spot metering can help with this if your camera has that feature.
