It appears to be a fungal infection called Maple leaf blister. Blisters appear on the leaves which are not always obvious. The rounded leaf blisters turn black sometimes lighter colored in the centers and the leaves become distorted.  The fungus is unlikely to threaten a healthy established tree. Remove the diseased leaves from the ground and make sure it has at least 1-inch of water per week. A severe infection can cause the loss of all the leaves but new leaves will likely appear within several weeks.
The is another fungal disease-maple anthracnose which looks similar but has irregularly shaped brown spots which follow the veins of of leaves. However both diseases are possible at the same time. The only way to make sure is to submit samples to
Delaware Cooperative Extension. The Kent County address is 69 Transportation Circle, Dover DE 19901.
Here are a few references:

https://www.canr.msu.edu/news/maple_leaf_blister_and_anthracnose_two_foliar_diseases_that_can_appear_on_s
https://ask2.extension.org/kb/faq.php?id=646190

https://hortnews.extension.iastate.edu/2009/6-3/leafblister.html