This symptom is hard to diagnose with certainty, but resembles herbicide exposure damage. Were any lawn or garden herbicides used in the area in recent weeks, or could a neighbor have applied one? Sometimes certain chemicals can be root-absorbed or evaporate into the canopy, affecting leaves still in development. Leaf stunting, discoloration, and distortion (twisting or cupping) can be typical symptoms for the kinds of herbicides that act like plant growth hormones in order to weaken or kill weeds. Dicamba, for example, is an active ingredient in many herbicides that poses a risk to tree/shrub roots if the dosage is high enough or if the plant is sensitive to that chemical. If it was an herbicide exposure, nothing can be done to reverse its effects, though if mild enough, the tree will outgrow the impact over time and subsequent new growth will look more normal.

If no herbicide was applied, it might indicate root stress or damage. Was any digging done on that side of the tree, or fertilizer or lime applied heavily, or is the soil on that side prone to getting extra wet or dry? While the tree is probably too young to have girdling roots impacting canopy health already, we can't rule it out. Is the tree's root flare situated at the soil surface, or could it have been planted too deeply, buried by a few inches of soil or mulch? Hackberry can have a few minor insect pests on the foliage which can distort foliage, but we don't see any indication they are/were present earlier this spring.

Miri