Polygonum species.

Just pulling it out by hand will get rid of it?
I can get the whole plant and roots in tug.

I had some thick Japanese Knotweed in the front beds of the house when we first moved in and I just painted them with RoundUp and it killed them all.
This is in the yard though and I don't want to kill the grass.

If the roots come up, that should be the end of it. Keep patrolling for new sprouts.

Roots do come right up, but its gotten to the point where its not viable to pull it all up by hand. There is just too much of it.

Anyone know of any spray that will kill it and not my lawn?

A herbicide which says it is for broad leaved (ie not grass) plants.

But it is not a typical lawn weed. It favours bare disturbed ground. So if it is growing in your lawn the lawn is too sparse. It would not thrive in a thick sward. If you can mow the lawn before the Polygonum seeds and improve the condition of the grass it will not be able to compete.

Yeah the spots in the lawn that it is growing are not as thick as the rest of the lawn.
When we moved in a 1.5yrs ago the lawn was a mess and was very thin and bare. I'm continuing to overseed each season to help build it up.

I will try a herbicide to see if it works.