Heat or not watering deep eoungh or maybe something else. But in this heat I've seen a lot of trees with browning leaves.

Best time to plant a tree in the fall last Oct on through the winter even.

I would suspect not enough water also, but cotton root rot comes to mind. Don't know if Red Oaks are susceptible, and don't know if your soil carries the pathogen. Oak wilt is another possibility, but I don't think it's as fast as you describe. New trees, this time of year, need heavy watering, especially if it's been dry where you are.

we had a tree die like that and the culprit was borers.after the tree died i just pulled some bark and i could see the tracks of the insects.

I had a neighbor in Miami poison a beautiful orchid tree that grew near her property line.....

Foul play?

Did you use weed and feed fertilizer? My first guess is not watering deep enough but you did not tell us what size it is and whether it came in the container or burlaped (dug up from field).

With container trees, you need to water moderately few times a week for how long, I don't know as it depends on soil type it's growing in, weather, etc.

Sometimes, weed and feed fertilizer can do a number on trees. It is not intended for lawns with trees. Even the small print says not to use around trees and shrubs but I see a lot of people do it anyway!

I had a nursery bought tree do that and when I dug it up I found a small plastic rope around the trunk that was under the soil line and was cutting into the bark. Since the tree receives nutrients and water from the layer right under the bark it was choking the tree. Apparently it had been balled and burlapped when the nursery received it and they planted it in the pot without removing the rope. They gave me a refund.