There is no reason to use Av mode for anything. Manual exposure will always give better results and is not slower. You set the exposure at the beginning of the game and leave it at that. If something crazy like the weather turning from full sunshine to a thunderstorm happens you can easily adjust the shutter speed or aperture, takes no time at all. I don't think Av mode has any advantage and for football or other sports it makes no sense at all. For sports you would use Tv priority because shutter speed is more important to freeze motion, but again manual exposure is less of a hassle than Tv and EC. Human perception of sharpness is based on contrast. Auto exposure overexposes leading to less contrast and softer appearance.
With the 1-series you can set your minimum shutter for example at 1/1000s in Av, so you can get up to 1/8000s if there is enough light, and like Neuro said, if a player drops in to the shadows or into the sun, you will never have longer shutter than 1/1000s, but always correct exposure.
And try to image just how incredibly useful this is at a concert with mental flashing lights.
"No reason to use Av" whatever...