Aperture priority is my preferred sports exposure mode for most, but not all conditions. "Athletics" in UK parlance means track and field to me, and I am pretty familiar with track and field shooting. There are many different athletic events, but Aperture Priority auto, used with the appropriate ISO level, is a good place for a beginner to start. First off, as others have said, you need to keep an eye on the shutter speed: if you have consumer-speed lenses like f/3.5~5.6 zooms like 18-55, 55-200,or 70-300,etc, the first piece of advice I have is to JACK THE ISO SETTING UP to at least 800 ISO. In bright light, this will cause absolutely no problems. In poorer light, like shadows, cloudy days,or early or late in the day as the light level is dropping, the ISO boost to 800, or 1,000 will be your best ally with consumer-speed lenses. Under bright,sunny conditions, even ISO 1,250 or 1,600 can give good photos with slower-speed lenses. A bit of noise but deep depth of field and a fast shutter speed is the absolute best compromise with normal, consumer-type gear and an inexperienced shooter.
With consumer-speed lenses like say the 55-200mm f/3.5~5.6 or the f/4.5~5.6 type 70-300 lenses, at ISO setting like 100 or 200, the exposure times even wide-open can drop to dangerously slow speeds like 1/250, or even slower, leading to perfectly-exposed, low-noise, smeared, blurry shots. While an exposure of 1/1000 second might sound fast, with a telephoto lens set to 200mm to 300mm zoom, that speed is not all "that fast". An ISO boost to make doggone sure that you have at least 1/800 to 1/1000 second will ensure stop-action shots that are mostly sharp, even with slightly bad technique, like snap-shooting, failing to keep up with the action as you shoot, and so on.
Standing at track level, on the field, is generally where I like to be. I know people always preach about using the lowest ISO, but with consumer-speed lenses, that is frankly lousy advice--you need to get the ISO ratcheted up to around 800 when using consumer-type bodies and lenses. Once you get to a shuttr speed of 1/1000 or faster, then you can consider stopping the lens down a bit, to maybe f/6.3 or f/7.1, which will give you additional depth of field, which will help provide what I call "cushion" for missed focusing, slower AF systems, and just,well, some "cushion" so that missed focus is not a killer problem.
I do not know what camera body or brand you have, but on some of the lower- to mid-level bodies, using more than one AF point, in Continuous AF mode, can often help the slower consumer-level lenses like the 55-200 or 70-300 find and track focus better than using just one, single AF point. Try and really pay attention to what you are doing, and don't let people chatter with you and ask you questions as you try to shoot.
Best of luck to you!