How to cap a very small irrigation system

How would i cap off a very small sprinkler system with manual shut-off (turn) valve? This is a non automatic system with valve located close to house. Yard is quite small, so no zones or dedicated meter.
Water is pooling around one riser head the small wheel in the water meter is turning. I probably wont need to cap off and abandon the system, but I’d like to know how to do it if I needed to. I hate to have this just pulling water and not know much about how to make it stop. Looking online, most systems I see are not nearly as simple as mine. They have timers and zones and backflow protecters. Mine is probably as basic as can be.

It may be a problem at the sprinkler head iself. I only noticed it when grass was cut. System hasn’t been used for many weeks as we’ve had lots of rain. Thanks.