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Quick leaf drop could be due to environmental issues; drought or root rot from to much water, drops in temperatures could also cause leaf drop.

A fungus disease could also cause leaf drop.

Drift from a Herbicide can also cause a quick death of plants.

Adjust watering if you determine this could be a cause.

Inspect the plants for signs of disease or insects. If you suspect this as a cause you can treat with Neem Oil.
Neem Oil works as both an insecticide and fungicide. It is safe for people and pets.

https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

Hi! Can we have a little more detail? Did you just get the plant, or move it? Are other plants in it's vicinity having trouble [it doesn't look like it, but it's good to cover the bases.] It could be from over- or under-watering; it sounds exactly like over-watering (leaf-dropping and yellowing), but yellowing is one of the most common symptoms in a plant that's stressed, and leaf-dropping has multiple potential causes as well. It's probably not under-watering, as it looks as though the entire plant is turning yellow, not just the bottom, and the surrounding plants look well-watered-and I somehow doubt you water your plants in a checked formation. :)

Without knowing the plant and the pest you are dealing with, it is difficult for me to tell you how to correct the issues.

We do recommend Neem Oil for most sucking insect infestations. It also works as a fungicide.

Neem Oil is organic and is safe for people, pets and bees.

https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

If you could provide more information, such as the variety of shrub and your growing zone.
If you upload an image,this will aid us in helping you diagnose the issue with your plant.

It would appear that the majority of your plant is dead. It may have been from the cold winter that nearly the entire United States suffered.
Though I'm not sure of the plant that is in the picture, it is possible it is just growing from the roots as they appear to have survived. In time your plant will fill in.

Depending on the type of shrub and the cultivator it could be a shrub that is grafted onto another root stock.
In that case the new growth may be different than the previous shrub.
If your wanting to give the new growth a chance, just go ahead and remove the dead material back to the new growth.
If your wanting to start over, early fall is a good time to plant a replacement.