If your pond site is absolutely flat and everything has to be excavated, like mine in Florida, then I'd say no way - you can't move enough dirt fast enough. Also, it depends on where your water table is - If I tried to dig an 8' deep pond with my tractor, it would be 5' underwater before I finished.
But. located in the foothills, you should be able to find a site where you will be making a dam, then filling with surface water supply (creek or runoff), and just doing some shaping. In that case, if you have lots of time and lots of patience, you can probably do it with your tractor.
Half a football field is around 150' x 100', which is about 1/3 acre surface area. Depending on how your banks are sloped, etc., if you have to excavate the whole thing it could be as much as 2,000 to 2,500 cubic yards of excavation (I didn't do the math, just interpolated a little from the 1600 yards I'm going to have excavated for my 1/4 acre pond). You'd be moving substantially less than 1 yard each trip.
$10K sounds a little high to me, although I don't know what it includes - if he wants to use a liner, for example. I've seen prices on the 'net for $1 to $1.50 for pure excavation. I'm paying $2.50 a yard, but that includes him loading, moving and dumping all the spoil to where I need fill (house pad, barn pad, 800' road, some low areas), compacting it and grading it. Total cost will be ~$4K, for a track hoe with 53' reach and a 1.5 yard bucket, D6 dozer, loader/hoe and two dump trucks.
I'm figuring it backwards - I can use 1600 yards of fill and I can afford the $4K, so that determines the size of the pond.