what is that?

here's a closer pic

you can see how rampant it is.

Last one

Your third photo looks like it could have been taken from my lawn! The brown patches are creeping bentgrass, which, when not kept mowed to 1" high, gets wiry and sports pom-pom tufts. I have been fighting the bentgrass infestation in my tall fescue lawn for three years. The first year I tried manually pulling it -- because it came out so easily. The grass is stoloniferous, however, so unless you get out every single root (which is simply impossible), it will regrow. The second year I tried Roundup. RU killed all the existing topgrowth and continued to suppress new growth for a good ten months or so, but then the bent returned. This year I'm fighting it with Tenacity. Tenacity is selective for bentgrass, among other weeds, and while it's killing off the topgrowth, it's too early yet to say if the Tenacity has truly eradicated the infestation.