SLR digital photography: Motion shooting needs blurred background. How can we make the background stand out or the foreground stand out?

It is required that background blur can be realized by using large aperture and long focal length. The background of sports photography can be adjusted according to different sports. For example, when shooting the Liu Xiang 1 10 meter hurdles, you can blur the background with follow-up, or you can let the athletes shoot with a high-speed shutter with a long focal length and a large aperture in front of the hurdles (the moving speed is relatively low) to achieve the effect of blurring the clear background of the characters.