I'm not very good on lawn type questions, but I think it might be what they call nutgrass or nutsedge:
https://www.ktrh.com/pages/gardenline_ne ... rass10.jpg
it is a difficult weed to control.
They thrive in waterlogged soil, and their presence often indicates drainage is poor, irrigation is too frequent, or sprinklers are leaky. Once established, however, they will tolerate normal irrigation conditions or drought.
The little nut things at the bottom from which they get their name are tubers. You really want to prevent it from making those tubers. If you can dig out the small plants before they have 5 or 6 leaves, it won't have made the tubers yet. If you keep doing that, eventually it will die out. They don't like shade, so if you can make shadier conditions, that will discourage them (but then you might also need a different kind of grass).
It isn't worth trying to poison them, because very few herbicides will affect them that wouldn't also kill your grass. And herbicides are not effective against tubers. So even if you found something that would kill off the leaves, the tubers would still be there and would just sprout again.
Sorry that it is mostly bad news!