Play it safe. Get one of each.
Nikon's D40/D40x/D60/D3000/D3100/D5000 (baby Nikon's)
do not have a focus motor in the camera body and can only auto focus (AF) Nikon AF-S, and the older AF-I lenses which have the focus motor in the lens.
The D80 and D90
do have a focus motor and screw drive in the camera body and can auto focus AF, AF-I, and AF-S lenses. The in the camera focus motor and screw drive is not used to focus AF-I and AF-S lenses.
Most of the AF lenses available as new today are yesterdays pro lenses and are not inexpensive, often being beyond the budget of D40 through D5000 owners.
The D40/D40x/D60 only have the Nikon Multi-CAM250 AF module and have only 3 auto focus points, non of them being a cross-type focus point.
The D3000/D3100/D5000/D90 all have Nikon's milti-CAM1000 AF module and have 9 focus points, the center one being a cross-type focus point.
None of the baby Nikon's have a top LCD, nor a second command wheel.
The D5000 and the D90 both have Commander Mode when using CLS.
Now then, shooting sports requires some specialized capabilities beyond most other types of photogrraphy. For shooting indoor, and outdoor night field sports, a good high ISO capablility is paramount, as is wide aperture lenses. Reach (magnification or longer focal lengths) is needed for field sports.
Of the cameras you mentioned, the D90 is what I would recommend based on your stated requirements:
It has:
- an in-the-body focus motor
- decent high ISO performance relative to its cost, and will be barely adequet to shoot indoor and outdoor nighttime sports if wide aperture lenses are used.
- has the Multi-CAM 1000 AF module
- has Commander Mode when using CLS.
- has a top LCD