I don't think these are salvageable in post to be honest. At least not at a level I'd be comfortable charging a decent enough price to make it worth the timeSeveral folks have talked about the main issue these show... the noise. I have a couple other ideas that I don't think are helping any at all. Consider them more food for thought for next time.
First off the lens. That's a pretty huge range of zoom, any lens with that much zoom is going to have more elements than a simple prime, and more elements means more chances for things to get micro misaligned, which means no where on it will be as sharp as the corresponding prime. With a tripod and a marked spot on the floor, there's no reason to use a zoom, let alone a zoom with that much range. You can rent a 50mm prime Nikon lens for $15 for a 4 day rental. You're charging parents greater than cost of goods for these pictures? That $15 is cost of doing business. Amortized across an entire team and you're talking a couple coins per athlete....
Second item, I could be mis-interpreting what you said in the question, but it feels like you locked in a focal length before hand and didn't re-focus from player to player. If that's not what you did, then a lot of what I'm about to write isn't relevant.
Just from these two images you can see a difference in where they were standing, one has the balls of her feet on the line, the other almost the heels are on the line. And how were they standing? leaning in? leaning back? that could easily account for almost a foot of difference between the two extremes. You were shooting at f4.5... but at what distance? and what focal length? Did you do the depth of field calculations to see how much wiggle room you had?
I haven't shot with a D90, so I'm not sure if you have the ability to do a rear screen live preview with a digital zoom, but if you do, in this scenario, it's worth it to use that to do fine tuning on each person you're shooting. OR, do the math and figure out a way to get foot or so of DOF either with a longer lens and more floor, or a tighter aperture.
Related to that... it's not going to directly alter the sharpness of the subject, but it will alter the perception of it if you can get the background far enough away to have it go out of focus. Again some time with a tape measure and DoF calculator will help get that figured out ahead of time. But the backside practically on the wall like these shots have is never going to get there without also risking having enough DoF to cover various depths needed for various people.