Looks very much like crabgrass.

Where do you live?

What kind of grass do you have?

How have you been watering? How often and for how long?

How high/low do you mow and how often?

@dchall_san_antonio I live Mansfield tx. I have Bermuda grass and I water twice a week half a inch each time. I mow the grass about 2 1/2 inches every three days. When I bought the house the grass was a disaster but I've fertilized and have put weed and feed but I'm new to it. It was looking great till the weeds started growing.

You'll have crabgrass & dallis grass there in Mansfield, it all used to be cattle ranches

Perfect. Thanks for the extra info. To begin with, fantastic job so far. All you need is a tune up on lawn maintenance. I have another question, now. Do you know what kind of bermuda it is? Did you put down seed or did it go in as sod? It looks like a sodded variety, and if you don't know that it is Celebration, then it is probably TIF 419. TIF 419 is by far the most popular warm season sod since about 1970. Here is a summary of care for established bermuda in order of importance.

Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall. Weed seeds need continual moisture to germinate. By allowing the soil surface to dry completely before watering again, you can prevent weeds. Of course Mother Nature might offer Her opinion on how much rain you need.

Mowing: Mulch mow at the mower's lowest setting 2x per week. If you wait too long then you should catch the clippings and compost them. If you mow 2x then the clippings will be short enough to fall back into the grass and not sit on top. When bermuda is mowed low it takes on a horizontal growth habit which is very dense and soft underfoot. The dense turf will help keep weeds out.

Fertilizer: Bermuda can take a high N, low to zero P and K, fast release fertilizer once a month.

In the winter it goes dormant. Resist the urge to make it green by planting rye grass. It might look fine all winter, but in the spring the rye can delay the awakening of the bermuda by many weeks.

Spot spray broadleaf weeds with a product like Weed-b-Gon or Weed-b-Gon Chickweed, Clover, and Oxalis Killer beginning in April.

Bermuda in full sun should never thin out. If you see thinning it is most likely that spot is getting too much shade. There is no sense reseeding or sodding the area, because the problem is the shade. Shady areas either need a different ground cover or a different approach (flower beds). Your new tree might become a problem as it matures.

Thank you for the advice. I will definitely change my wattering habit as well as adjust the height on my lawn mower. Hopefully next year my grass will be more dense and can keep the weeds out. I've always liked the look of my grass when it's mowed taller but I see with Bermuda it shouldn't be that tall. As far as the type of Bermuda I have no clue which type it is but I do know that it went down as sod.

Sod equals either TIF 419 or Celebration. Do not be tempted to overseed with bermuda seed, either. Bermuda seed is all common bermuda and not the hybrid TIF or anything else. They are like distant cousins.

You can use a preemergent herbicide this fall and again next spring. Timing for the fall app is not well understood, but I would apply on the day of the first big rainfall after the summer heat breaks. For the spring app put it down when you see forsythia blooming in your neighborhood.

The grass will never be dense enough to stop those weeds, get on a consistent pre emergent schedule & stick to it religiously. Any rogue weeds that make it through the preM barrier, give them a quick spot spray with your chosen selective herbicide. There's a million out there, but I prefer sulfentrazone based as the 2,4d based chemicals stress the bermuda pretty bad.

The grass will never be dense enough to stop those weeds,

Sadly bermuda looks best when mowed very close to the ground. If there is any flaw in the "canopy," that can let in enough sunlight to the soil that weed seeds can germinate.