How about situations like this where a flash is inappropriate? Any other work-arounds in post-production or other camera settings (white balance, metering options) that might reduce it?OR, Is this just a function of the higher ISO sensitivity? I shoot in gyms like this all the time (7D/1dIV) using 1/800-1/1000, up to ISO 3200-6400 and have never seen it. Have I been 'lucky' that my shutter speed and the frequency of the flickering just have not been in synch, or has my camera been unable to detect it at these lower ISOs?
Based on my understanding this is solely a function of shutter speed. It's similar to the rolling shutter phenomenon and this would probably not be an issue with an electronic shutter. Your mechanical shutter does not expose the entire sensor at once. One curtain opens and another closes behind it. With fast shutter speeds both of the curtains move simultaneously. So the sensor is exposed in "slivers."
A portion of the "slivers" being exposed are darker and have a green color shift because the fluorescent lights had cycled while the shutter was in motion.
The article on focal plane shutters at Wikipedia has a diagram showing the function of the shutter. Based on my understanding, the aperture and sensor sensitivity will have little if any effect on the banding.
Gyms can have a variety of lighting types and not just fluorescent which might explain why some people don't see this or don't see it as often.
I've shot basketball and volleyball in gyms and never had an issue. I only discovered this issue when shooting at my son's karate school. Shooting at 1/160 gets me a large number of keepers and I don't see anything at all at 1/125. Flash kills off the banding completely. Now if I could get the instructor to get rid of the bright blue and pink mats which makes getting reasonable skin tones almost impossible...
The banding in the OP's photos may be attributed to a rolling shutter type effect, but having an electronic shutter wouldn't completely solve the problem of shooting under flickering gym lights. I have many hundreds of photos I've shot under these sorts of lights where the brightness and WB vary across the frame perpendicularly to the direction of the shutter movement (and thus cannot be a rolling shutter effect). The lights don't all flicker exactly in sync, which means for fast shutter speeds you'll often see variations due to the lights being in different parts of their cycle from each other.