As soon as I have grass I well remember that.
Do you have a mower with a bag? Use the bag to collect the chopped grass from the mower exhaust and then dump these pilings on the muddy/nongrass area...grass will start to grow in about a week, and every time you cut the grass keep putting it over that area it will grow faster...its similar to putting hay over the area but the cut grass is cheap and free to put over all you have to do is mow the lawn.....