In most cases, raising ISO in-camera is better than underexposing and pushing the RAW later.

Why: noise is mainly caused by not capturing enough light. If you underexpose, the signal is weak, and brightening later boosts both the image and the noise. Using a higher ISO doesn’t create light, but it amplifies the signal earlier in the camera pipeline, which usually gives a cleaner result than a badly underexposed file pushed 1–2 stops afterward.

That said, the best fix is always more light: open the aperture if possible, slow the shutter if motion blur is acceptable, or add light.

Practical rule: for action, first choose the shutter speed you need, then use the widest aperture available, and raise ISO enough to get a proper exposure. Avoid unnecessary underexposure if image quality matters.

Exceptions exist with some modern cameras at certain ISO settings, where modest RAW pushing can be similar, but as a general guideline, expose as well as you reasonably can in-camera rather than planning to “fix it later.”