Need more information.

Where do you live?

What kind of grass do you have?

What is your watering regimen? How often and for how long do you water?

Do you have low spots that tend to hold water for days after a rain?

Do you ever toss garden trash on the lawn and leave it for a day or two?

I Live in Pittsburgh, Pa, and Idk what kind of Grass is in the back .I am OCD w my front lawn Lol but KBG def, I never water the back lawn, I have a Lab and again just kinda obsessed w my front lawn, but would like to not have it come back every yr, No rain stays there either, and and never throw trash on lawn, just my Labs poops on the lawn and pees but this is def a fungus and looks exactly like brown patch, Thanks

Usually disease comes from too much moisture, trapped dew, or fertilizer issues. I'm drawing a blank on prevention. Let's see what others think.