These are the flowers of the grass. you must have let it grow a little longer than normal so they have flowered. just mow them off.

On the other hand, it might be annual blue grass (Poa annua). It is hard to distinguish from other grasses in its early stages, but in mid summer, it goes to seed and dies, marring the appearance of the lawn if there is too much of it. Annual bluegrass can flower at only 4 cm tall, while standard bluegrass (Poa pratensis) usually needs to get around 15 cm tall to bloom.