Fast shutter speed freezes action, larger aperture (small F number) blurs background.
Try to keep subject and background far apart so background's focus plane is not close to subject's. Longer distance reduces blur and longer lens increases it.
Use continuous focus, dynamic area or 3D centered on the subject.
You can also get good effect if you learn to pan. If your subject is moving predictably, move the camera with the subject. The background will blur from movement. If you pan well you can slow down shutter speed some. Panning well takes practice.
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Try to keep subject and background far apart so background's focus plane is not close to subject's. Longer distance reduces blur and longer lens increases it.
Use continuous focus, dynamic area or 3D centered on the subject.
You can also get good effect if you learn to pan. If your subject is moving predictably, move the camera with the subject. The background will blur from movement. If you pan well you can slow down shutter speed some. Panning well takes practice.