If even one of your sprinklers isn't moving across the lawn the way it should, your grass is not getting even water distribution and this could lead to patchy areas of the yard that will be unappealing. Oscillating sprinklers may stop moving for a few different reasons. \
The quicker you can identify why the sprinkler isn't moving, the quicker you can give your lawn the moisture content it needs. \
Check the distribution cylinder. If this is not centered, it will prevent the sprinkler head from moving the right way. \
Low water pressure, high water pressure, kinks and crimps in the hose, a clog on the nozzle, and debris surrounding the sprinkler head can all keep the sprinkler head from rotating the right way. \