Sugar Tyme Crabapple
What you have observed probably isn't a cause for alarm. So far as we can tell from viewing the photo, the leaves do not show evidence of disease or insect damage.
Some leaf drop and yellowing is often evident on newly planted trees and shrubs. It's a consequence of transplant stress and adjustment to a new location/environment.
Watering well during dry spells is important. Go here to learn more about watering: