Panning is something any sports photographer should have nailed. The technique involves moving the camera with the subject, keeping it in focus while blurring the rest of the image. Panning portrays a sense of speed and motion otherwise impossible to portray in a static image.
When first starting out, expect to get a lot of unusable shots. Panning takes practice and it’s all about technique. Each time you try though, you should notice your success ratio rise. The speed your subject is moving will designate the shutter speed you can get away with. The slower the subject, the slower your shutter speed will need to be to get the same degree of motion blur. Experiment a bit and you will get an idea of where you need to be, 200/250th of a second is a good place to start with motor sport. Keep in mind that the further you zoom, the more exaggerated the effect is also.
The best tip I can give after my own trial and error is to follow through. Get your subject in the frame slightly early and follow it after you have taken the photo, hopefully creating one smooth motion. This may also give you an opportunity to grab a second shot each pass too. Stand with your feet solid, elbows tucked in and camera pressed to your face and you should be able to keep the camera where you want it.
Once you have a good pan or two in the bag, try and outdo yourself with a slower and slower pan. Some of the best pans I have seen haven’t necessarily been the sharpest shots.