[cicopo]

For those who are a bit confused about using shutter speed to capture the action but still get some background blur vs using a wide aperture for the blur as is commonly used in several areas of photography we have to consider this. Using a wide aperture (f 2.8 or f 4.0) forces the camera or operator to use a fast shutter speed (too fast in good light) for any kind of prop blur plus cuts your chances for a good photo because you may have a very shallow Depth of Field (DOF). Action is best shot in either manual or Shutter Speed priority and depending on the venue you use shutter speeds as needed while following the movement. Prop planes & wheel sports generally need slower shutter speeds to capture a sharp photo of the plane or car / motorcycle etc BUT blur the prop /wheels & tires & background to show motion. Freezing the action at a car race makes it look like the car is parked rather than at speed. Fast shutter speeds work for jets & most people sports like track & field / football / soccer etc. It's a matter of understanding what style of photo best portrays what was going on.
The way I've done it is by selecting my shutter speed based on experience gained over the years & letting the camera select the aperture BUT I check my exposures regularly (sometimes not often enough) & use exposure compensation to fine tune for backlighting or overcast issues AND I adjust my ISO to try & stay away from very small apertures (f 16 & up) to help prevent sensor dust from showing up in my images. As my panning skills improved I've lowered my shutter speeds but I also rely on lots of shots to hopefully get a few really crisp ones. I've also upgraded my equipment along the way too, and for now I've got equipment that exceeds my skill level so buying the newest bodies won't really help my keeper rate.