a method that provides very neat results is to drag shutter and pop flash ,to freeze subject but still get great shawdow detail and blur.
try setting the apeture for a certain distance to flash balance. say at 10 ft your f8.
Measure the background and it may be F8 at 1/4 second.
Set your apeture at f8 and then set your shutter for 1/4 second.
When your subject moves into the 10 ft sweet spot , fire off your camera.
The flash will take care of the subject that is in the 10 ft range and your shutter will compansate for the ambient lighting .
this technique is good with a tripod.