What type of pump and HP? Any model number? Is there a pressure tank? Is this well used for irrigation only? I've provided more information than you asked for so the job would be well though out with good results.
18 GPM is an awful lot of water. Impact rotor sprinklers are about the only way to get that much water unless you have very large pump, say 7HP. You'll be flooding the court when you mainly want it damp. Sprinkler ratings is usually at 60 PSI and you would need a pretty big pump to provide that much water for six sprinkler heads. I would suggest rotor type sprinkler heads. They are adjustable, can get a good distance with a fine spray pattern.
I assume the sprinkler heads would need to be place at the perimeter of the court? You may want to use rotor style. They provide more water at a greater distance. Most sprinkler heads can be adjusted for water flow. With pop ups there is a small screw that you tun to restrict water flow. They are set to the highest output from the factory. Rotors and some impacts are also adjustable with an assortment of nozzles to regulate water flow.
Pipe size wise. Most irrigation pumps use a 2" output pipe size. If it is submersible, increasing the pipe above ground may not help much. 3/4" I'm assuming is it a submersible and I do not know what is black IPS line is and I'm assuming it is poly pipe. To increase the pipe size with poly pipe may be difficult to find adapters to get to a larger pipe. What would the distance be from the well head to the court?
Increasing pipe size may help if it is a long distance. Ideally you want the largest pipe possible to the feeder (main) pipe. Usually 1" or larger. Reduce to 3/4" to the sprinkler branches, then 3/4" or 1/2" to the sprinkler heads.
To get an even distribution of water, the pipe would need to be tee-d off the main and loop around the court in both directions and connected as one loop. I like to call it a lolly-pop. This would help provide an even amount of water to all sprinklers. if the pump is too small, a controller and zone valves would need to be added and to allow 1/2 the court is be irrigated, then the other half.
This is a pop up