A photo or more description would be helpful, that said it is perhaps a slime mold.
https://www.gardeningknowhow.com/lawn-care/lgen/black-substance-on-lawns.htm

A person with a lot of gardening experience identified the stuff in my lawn as black slime mold and it matches the pictures online so I am pretty sure that is what it is.  I started about 10 years ago in a small area that did not get much traffic but last year it started to spread and this year it is in the grass over a 100  square foot area.  The adults and kids hate it. It looks terrible and feels terrible to bare feet.  At the rate it is going it will soon spread throughout  my lawn.  How can I get rid of it?  Thanks for your help.

Thanks for your response.  Unfortunately it dose not fit my situation.  Can we try again?

The soil is mostly sand.  The grass grows but it is never lush. It is in full sun.  Over the last several years, I have tried less water which slows the spread of the mold but results in a ugly patchwork of brown parched grass with black blobs of mold.  Last spring I tried blasting it with water.  That was the wrong thing to do.  It encouraged growth and spread it!  I need to do something that will kill it and not the grass.  Do you have a recommendation?

Here is a link to Slime Mold. Please read it and look at the photos. Then we can decide if it is actually slime mold. Also, photos are needed. We cannot help without that type of information.  https://extension.umn.edu/lawn-care/common-fungi

Photo attached as requested.

Here is information on your problem: https://www.gardeningknowhow.com/lawn-care/lgen/black-substance-on-lawns.htm