Steve Perry wrote:
I love my D850, but for the scenario you describe, the D4s is the better choice. When it comes to low light, the D850 is OK, but the single digit pro series bodies are made for it. As long as you're (at least mostly) filling the frame, you'll like the D4s. The only real downside I can see for sports shooting is that the D850 does have the newer, better AF system, but the D4s is no slouch. If it were me in that scenario, I'd get the D4s.
Having used the D4s before I upgraded to the D5, I would have to agree wholeheartedly with Steve's comment. I also use a D850 for sports, which I find to be much more useful that my D810 (former camera). I will admit that I will sometimes use my D500, but I agree with the others on here that it has nowhere the low light capability of the D3/4/5 series, which were essentially designed and built for sports action work. Best of luck.