I have what I believe is some kind of fungus growing in my lawn. It looks like fecal matter.
Fungus Growing in My Lawn
It is best to cut out a section and take it to your local Extension office or perhaps nursery. Have them take a look and see what they recommend to use to get rid of it. There are many very good fungcides on the market that should take care of the problem. As with any such attack, the sooner it is sprayed to gain control the easier it will be to gain that control.