Weed on my lawn
Thank you for your email to eXtension.
The plant appears to be one of the pigweeds, although it's difficult for me to tell without it flowering. These tend to be annuals, so if you can keep mowing it and preventing it from flowering and seeding, it hopefully won't come back next year.
I would recommend trying to spray this with one of the broadleaf herbicide mixtures that contains 2,4-D, MCPP, and dicamba (one example is Trimec). If you've used this product without success, switch to a product that contains triclopyr in the ingredients (it's often mixed with 2,4-D). Remember to read and follow all label directions.
Please let me know if you have any further questions.