Double check the 48-foot measurement, this is inside to inside of the backboard.
Take a long string and run it against the side of a pitching platform all the way to the opposite pitching platform. The sides should line up square.
When the platform is in place, spray paint completely around the edges for a reference (image 1). Move the structures to the side then remove the sod from the area; add more soil if needed to make the area level. Add some extra soil where sand pit will be. Put the structure back into place and check for levelness.
The stake needs to be 48 inches in front of the backboard, and centered in between both pitching platforms, stand 15 inches tall and tilt slightly forward. Dig hole to set bucket, go as deep as you need to get to 15-inch height (image 2). If you have extra concrete, pour it dry around the bucket before backfilling with dirt.
We placed a cap on the top of stake for safety reasons. Fill the pit with play sand and start playing.