The leaves are exhibiting symptoms (misshapen leaves, spots, etc.) of some fungal diseases such as scab, leaf spots, possible rust, etc. These diseases can be common in cool, wet springs. You will also see leaf drop. Other issues may include drought, excessive rainfall, etc. No chemical controls are recommended for ornamental trees.
The tree also looks like it is leaning toward the house/deck.  Make sure it is not a hazard.

All you can do is water during dry periods and rake any fallen leaves and discard in the trash. In the future if you decide to replant, look for disease resistant varieties of crabapple. Take a look at our web page on ornamental fruit trees for more information https://extension.umd.edu/hgic/topics/ornamental-fruit-trees-preventing-diagnosing-and-managing-problems
Here is some information on how to decide when to remove a tree https://extension.umd.edu/hgic/topics/how-do-you-decide-when-remove-tree

 You may also want to contact a certified arborist for an onsite diagnosis regarding the Health of the tree and its structural integrity and the best way to proceed. http://www.treesaregood.org/

Marian