A sprinkler head riser is a 1/2″ threaded nipple that can be cut to length to connect the sprinkler head directly to your lateral line. This is old-school technology. If your sprinkler system has these and you have not had a leak yet, you will. When a zone comes on and there is a stream of water shooting straight into the air and your sprinkler head is lying in the yard, you most likely have sprinkler head risers.
To solve this problem, install a swing joint. Dig up the leak and where the sprinkler head riser connects to your lateral line, remove it. Install a 1/2″ or 3/4″ swing pipe ell to the fitting in the lateral line and on the bottom of sprinkler head. Attach a piece of swing pipe at least 12″ long to the swing pipe ell at the lateral line, and to the ell on your sprinkler head. Bury your head and adjust it. This will prevent the joint from breaking in the future, unless something extreme happens to it, such as being run over by a vehicle.