I built two stadium lights. Placed on opposite sides of the field they do a nice job of lighting a decent size practice area for 10-12 kids. For a larger field or different sport, you may need several more. Each light draws ~.750 Amps, the Dewalt pack is good for 2.3 Amphours or not quite 3 hours. Still more than long enough for practice.
Needed 36 Volt Dewalt Lithium battery pack
These things are great, lightweight, fast charging, and very convenient after you have followed the directions to add standard power out wires. I will not detail how to disassemble the battery as this is readily available on the internet in several places.
9 STAR LEDs (3 watts ~100 lumen each now available direct from China for around $2 per LED, ebay and other sources)
Most of these high power, high efficiency LEDs operate from 3.5 to 4.0 Volts. To save money we are not going to use the recommended constant current driver, but wire directly in series. (36 V / 9 LEDs) = 4.0 volts per LED.
CPU style heat sink
1 ohm, 10 watt resister (to add some safety margin)
18 inch long piece of aluminum angle (1/16" by 1 inch)
JB Weld Epoxy
1 inch hose clamp
10' x 1/2 pole (PVC pipe)
Screws, wire, solder