Here is what the professional photographers use:
Shooting action in low light all depends upon how low is the light.
Lots of things to think about.
How bright is your brightest lens?
F2.8 is about as bright as it gets for a zoom lens.
Most zoom lenses will lose brightness as you zoom toward your target.
The ones that don't, are very expensive.
Trial and error is your only way to find out if your equipment is adequate:
Set the camera for aperture priority, set aperture to brightest for that lens, set ISO to the maximum, then take a sample shot.
View the resulting photo.
Is it bright enough?
If not, you are in trouble.
If brightness is OK, view the settings for that photo.
That will let you know if you have extra margins for adjusting ISO and/or Shutter Speed.
I'm taking the pictures for a high school soccer team and the games are usually after the sun is down. Typically the fields are not well-lit. I'm new to photography, so any suggestions on ISO, AV, shutter speed, etc. settings? I have a Canon Rebel xs with a 55-250 mm lens. Thanks!