I think you might need a K20 expert here, I haven't used one but from what I've read it does some fancy sensor stuff which is different from the usual digital photography HDR process. Sensor sensitivity changes to suit the bright/dark areas which is interesting and could possibly be used for sports but I don't know the details.
The 550D would still use the old process which is definitely not suitable for sports:
HDR = High Dynamic Range, which in itself doesn't really mean anything without context. In terms of digital photography HDR usually means capturing a greater range from the brights to the darks than you usually would be able to capture (or view on a standard monitor) and compress the brights and darks so you end up with an image where both the brights and darks are exposed correctly. This an be very useful for certain situations, eg. a sunset where you want to capture detail in the dark rocks in the foreground and also the bright clouds on the horizon.
Assuming you're using the in-camera HDR function:
Usually the method used for this is bracketing, taking multiple photos that expose the dark areas and bright areas correctly then merging them into one image with an algorithm that keeps the properly exposed dark and light areas.
As the usual method to make a HDR image is by taking multiple shots, anything that moves between the shots will be an issue, not to mention that when exposing for the darker areas the shutter speed will slow down a lot and may also blur fast moving action.
You can only really use this if nothing moves while the multiple exposure are taken, this includes you holding the camera, and anything in the frame (people, cars, animals, trees, water, etc.)
There's sometimes a small tolerance for movement but not enough for standard handheld shots of people moving, definitely not sports or anything moving quickly. Most HDR shots are taken using a tripod, usually of landscapes/architecture/things that don't move.