ELNikkor wrote:
Since the D500 with the same lens is basically just cropping each photo, why not save the money and crop each photo that needs that "extra reach"? ....!
Because the D500 gives you a 20... well almost a 21MP image.
When images from the 24MP D750 are cropped down to DX size, you're left with 10MP images. Having used 8MP cameras for sports in years past, I can tell you that leaves you without much to work with for any additional cropping or other image editing.
Some years ago we did a head to head comparison of an 18MP crop sensor camera versus an equally cropped image from a 21MP full frame... same lens, same subject, same distance. The difference in quality was very apparent. The uncropped image from the crop sensor camera was a great deal better than the cropped image from the FX camera. If it were a higher resolution FX camera like a D810 or the new D850, it would be a different matter. But it would not be a good thing to crop 24MP images down to DX sizes.
I suspect the D500 can give the older D750 a run for its money with high ISO performance, too... That will be important for night games.
Finally, does the D750 have "Flicker Reduction" feature? Depending upon the field lighting, this can be very be important. I'm almost certain the D500 has it. D7500 does, too (actually, I think D7200, D7100 and D7000 do, too... but check to be sure).
What Flicker Reduction does is detect the cycling of those types of lighting and then time the release of the shutter to the peak output of the lighting. I think some older Nikon had it for video, but not for still photography. More recent Nikon (and Canon... other brands ?) allow it to be used for still photos, too. The "old school" methods of dealing with fluorescent, sodium vapor and similar lighting that cycles was to use a slow shutter speed (usually not an option with sports) or to take lots and lots of extra shots because at least half of them would be poorly exposed and have ugly color casts. The exposure problem cannot be corrected by using manual exposure and the color shift cannot be corrected by setting a custom white balance.
I have not used Nikon with the feature, but on my Canon the Flicker Free feature works great... reduces the number of poor exposure/off-color shots to less than 5% (as compared to about half of shots or more spoiled, without the feature).
Timing to the light cycling with the anti-flicker feature causes a very, very slight delay in shutter release... Usually isn't noticeable during shooting, but occasionally will be. It also might slow frame rate a wee bit at times. So remember to turn it off when not needed.