Hi, 

It appears to be a type of turf mushroom. If you have a tree removed and the roots are still in that area, typically that is the cause for the fungal growth, on the decaying matter under the surface of the lawn. Even if the tree was removed before your presence there, it can take a number of years for the roots to breakdown under the surface. 

There isn't a treatment that is warranted as the mushrooms will re-grow until the roots are decomposed. While these fungal growths are technically not 'fairy -rings' you can try the management techniques described on the webpage to attempt to have them dissipate. Hand removal of them is fine, and trying to establish a thick turf by aerating compacted areas and overseeding in the fall are the best steps you can take to have healthy turf grass. 

Let us know if you have further questions. 

Emily