It looks like a broadleaf weed, possibly buckhorn plantain. The link below can help you identify weeds. Broadleaf weeds have taproots but are among the easiest to kill just don't let it or any other weed go to seed.
any broadleaf weed killer will work...i.e. weed-b-gone (spray works best).
If you havent put down a pre-emergence yet, any other weed seeds you have in the lawn will continue to germinate and come up throughout the year. Easier to prevent from coming up than continue to spray them all year.
At first glance it looks like wild lettuce or some monster dandelions with no flower or seed head.
What ever it is, it is a broadleaf and can be controlled with a broad spectrum herbicide like Trimec or weed b gone. I prefer Trimec because it has 2,4-D and Dicamba. It is fun to hit weeds like that and watch them wilt up.
The main organic approach is get your shovel and dig them out! Be sure to fill in the hole and replant grass seed, other wise it will just get more weeds.
Vinegar is herbicidal and you can spray it on weeds. It tends to kill the leaves, but not the roots, so they can grow back. Vinegar and salt solution is more effective, but you don't want to get salt in your soil, it will keep everything from growing.
I use herbicidal vinegar on dandelions with great success. I go out to the yard in the early morning when the soil is moist and using a "dandelion tool" pull the weed up trying to get as much of the taproot as possible. I then spray the hole left in the ground with the vinegar to "burn" the remaining taproot.