You can:

right click on the clip, choose "inser velocity envelope", drag down to zero. But to have motion, then freeze, then go back to motion you have to add points to the envelope and adjust the speed at the correct locations.


I find it faster and easier to freeze one frame by slimply putting my cursor on that frame, then go to the preview window and click the disk icon (make sure preview is set to best and display at project size is on) save frame as a still file, then drag that still back on your timeline and adjust the length.