In this case the problem is not caused from movement of the sobject, but it is more likely caused by a double exposure, the first caused by flash light and the second formed by ambient light. You can solve this problem closing diafragm. If you want to keep lens open and flash light you can chose HSS or a ND filter.Usually flash is faster then any shutter speed, and it is flash light that freezes the movement.
True in a studio. Not so true for fill flash on bright summers days.
In this case the problem is caused by camera shake because the flash enforced shutter max synch speed of 1/200th is too slow.
It is not a double exposure, it is a question of mixing and balance flash with ambient light.
Closing the diaphragm will give the flash more work to expose at all, and make it tricker to reach an ambient / flash balance, the result is likely to be dark background and caught int headlights subject, flat batteries and long recycling time.
HSS is probably part of the answer, although for fill flash against bright daylight you probably want to keep the power up, HSS will diminish the power.. A monopod is probably the other part.