There must be a huge mycelium run under the grass.
Back in the day [any FBI that read this: back in the 90s] I grew a few rounds of “magic” mushrooms. Not to get high; I did it for the sheer sciency joy of the process. Cue Ray Wylie Hubbard: “I didn’t use the cocaine to get high, I just like the way it smelled.” But one time I had a big jar of rye grass substrate that wouldn’t fruit so I finally threw the contents into my neighbor’s manure pile, just in case. 2 years later they had giant flushes of Cubensis this size. I snuck over the fence again, with a styrofoam box full of dry ice, and collected what must have been 2 lbs of the darned things. Because I didn’t want them to be embarrassed if they realized what they were growing, good neighbor I am.
I don’t know what those are, but I won’t be eating them. The deer haven’t touched them, and that’s a bad sign.