You need to start with a very fast ISO speed to stop sports
action in dark gymnasiums.
There is a quality difference connected to ISO speed, and there
are some creative factors to be considered, but generally the slower
the ISO speed the smoother the tonal quality of the finished photo.
With digital media the higher ISO speeds translate to more ‘’noise’’.
It’s usually advantageous to use the slowest ISO speed possible to
make a photograph.Outdoors in bright sunlight an ISO of 100 or 200
is a good choice. At the beach (with white sand) or when the ground
is covered with snow ISO 100 would be a better choice. If your subject
is in the shade a 400 ISO or even 800 might be the better choice. In your
home or, say, a school gymnasium you will probably need to shoot at a
higher ISO, say 1600. You may even need to set your ISO speed to 3200
if your camera allows it.

It’s best to experiment by taking photos you really don’t care about than to
try different speeds when the photos are important to you or your family.