With sufficient light, you can shoot anything free hand, even without image stabilization. Your hand can only move so fast and shutter speeds can often get very quick.
The XS-1 has a 1/4000 shutter and the lens goes to the equivalent of 623mm for a 35mm camera.
The general rule of thumb is that the shutter speed for free hand should be somewhere between 1/focal length to 1/5*focal length. Even taking the most conservative version of this, 623*5 is only 3115.
This means that 1/4000 shutter speed is fast enough to take a free hand photo at the max zoom of the X-S1 even with the image stabilization turned off. So if you have enough light for 1/4000 shutter speed or probably even 1/3000, you are fine without IS on. Depending on the strength of the IS you might be able to even get down to around 1/600th second exposures without a tripod.