Shooting a stage play with Nikon d 100 is very virtual. Is it necessary to increase the shutter speed?

According to your explanation, it should be caused by the slow exposure speed.

Generally, you don't want to be disturbed by the flash when shooting a stage play, and you can only solve it by improving the shutter speed and sensitivity.

As I don't know your specific amount of light, I can only make some simple suggestions:

1.

Put the ISO of the camera

Changed to 1600

2.

Change the camera to aperture priority and maximize the aperture, that is, the aperture value is the smallest, that is, less than 5.6.

Look at how the photo was taken.

If in doubt, please ask.