Turfgrass dieback can be difficult to diagnose, especially from photos and well after the symptoms began, since other conditions can then obscure the original symptoms and pattern of symptom development. You can see how what you're observing compares with the most common fungal disease symptoms on our Diseases of Home Lawns page, as well as common insect damage symptoms on our Insects and Mites of Home Lawns page. For example, digging into the soil a few inches deep in the dead zones could rule-out whether abundant white grubs are a likely suspected cause, and whether the dead grass blades in those spots are still firmly attached to roots or are detaching due to either root rot or grub feeding earlier in the season.

Turf diseases and insects typically have fairly seasonal impacts, meaning that they only cause visible damage or symptoms at certain times of year due to environmental conditions (like a temperature range or with reliable moisture from rain, dew, or very high humidity). It's possible more than one issue is overlapping if you've seen symptoms carry over or worsen from one season to another, or the cause may be abiotic instead (that is, resulting from environmental factors and not a pest or pathogen). For example, most of Maryland (and probably all of Delaware too) has been in a notable drought for the past two years, so depending on how the lawn was being monitored for watering needs or irrigated, that can influence how likely a pest or disease outbreak can be.

Turfgrass seed packages and sod are usually blends of more than one turf species and variety, and sometimes one of the components of a mix is more vulnerable to issues like infection, pests, or weather stress than the others. Some of the grass pictured looks a bit like Kentucky Bluegrass...do you recall what the components of the sod were? (Was it tall fescue, or was it Kentucky Bluegrass?) The majority of sod produced locally is a mixture of tall fescue and Kentucky bluegrass. The spreading growth habit of the Kentucky bluegrass knits the sod together, but since it can be more vulnerable to problems common in the mid-Atlantic compared to tall fescue, it generally only comprises about 5-10% of the mix. Some suppliers do grow pure bluegrass sod, though, which is why we ask.

We're not certain what weed you're referring to as "spider grass" (maybe Bermudagrass?), but agree that its presence is probably  not related to the dieback, other than the areas of dead turfgrass foliage being opportune places for that weed to colonize due to the lack of competition.

We can try to narrow-down a cause for the browning, but a few more images of the lawn overall (to better see the pattern and extent of damage) and more information about its general care since planting will be helpful. Was the lawn overseeded each autumn since it was installed? If so, do you recall what seed was used? (For example, were any varieties on the bag's contents label on the list of recommended cultivars from local turf trial facilities? Or do you recall what approximate mixture of turf types it contained, like tall fescue with fine fescue, or another combination of species?) Does the area have any root competition from mature trees within, say, 50 feet of the lawn? Does the soil in the lawn drain well, or ever tend to get soggy for a day or two after heavy rain? Are any of the patches of dieback near a downspout outlet, gully, or other water source? Are there any dogs that could be urinating on the lawn?

Miri