@Frederic for the sharpest action shots, use shutter speed priority, not aperture priority. Aperture priority is better for portraits and landscapes. Lock it in at around 1/500 or 1/1000. Set your metering in the camera to center-weighted. This will allow your camera to adjust exposure best for what’s mostly in the middle of the frame. Make sure your camera is not on spot metering. I would leave ISO on auto.
If you want a deep depth of field, set your camera in manual mode with shutter speed of 1/500 and aperture to F20 or 21. ISO on auto. This way everything in the distance will be sharp as well. On bright sunny days you should be able to pull of great well exposed and sharp shots with these settings.
The reason you have ISO on auto is because the sun and your position keeps moving and with auto ISO the camera will automatically try and get the best exposure. You don’t have time to adjust this when shooting. The Centre weighted metering will help in your camera to guess the right ISO setting.
Hope this helps.