Unfortunately, "sports" and "budget" are mutually exclusive.
If he is looking to do SI-style "ball in the air" type shots, you're going to have serious trouble getting anything worthwhile for football in the $400 range. However, if the understanding is that he learns to use it and then upgrades the lenses to handle it, that D70 is great.
The D70 can mount any lens, including the 80-200 AF-D f/2.8, which could really do a passable job as a very basic professional kit. The lens is about $500-600, but it's really sweet for that kind of work.
There's a reason all the photographers on the sidelines at the games have massive gear. The most important thing, to my eye, about great sports photos is isolating the subject. Often this means getting the background to blur and fade into the... well... background. And that requires big glass, there are few, if any shortcuts around that.