Hi Bearcat1: I would question if the use of a drone - even with a good camera such as that on a
Phantom 4 Pro - is what you need. For a start, drones use cameras with a very wide lens. This is not what you want to show fine detail for learning about sports technique improvement. And that's before any legal or health and safety considerations. Or the disruption to the football player's concentration, as drones are noisy and intrusive.
What you need instead are three or more video cameras positioned at different points around the pitch. They could be on tripods and/or attached to existing infrastructure to add varying height perspectives. Battery length won't be a problem. The cost will be the same as a price of one drone, or less. You will have much, much more detail to assess. Alternatively, simply have one video camera on a tripod with a decent operator to follow the player (which will be approximately one third of the cost of a drone).
Drones have their uses, but these are often exaggerated and often not the best choice. There has been much talk of using drones in wildlife conservation for years, for example, but the hard reality is different and somewhat limited.
Elite sport professionals, who all recognise the value of filming to detect detail and enhance performance, use ground-based video capture. And, of course, they use software to help isolate and calibrate the relevant detail. This is where I would suggest you might better focus attention, not on the use of a drone.
All the best - and Merry Christmas.