Japanese beetle? What is eating my tree
This is possibly Japanese Beetle damage, but judging by the distinctive shot holes (holes in the leaves surrounded by dead tissue), I'm going to say that it is flea beetle damage. Apple flea beetles, which are shiny green or blue-green, do attack crabapples. They fly when disturbed, so you may or may not have seen them. Because they are similar in color, but much smaller, they can be mistaken for Japanese beetles from a distance.
Here is a CSU fact sheet on flea beetles in general, with photos of shot hole damage, as well as a photo of more advanced all-over leaf damage. Life cycle of the apple flea beetle and controls for the adult and larval stage of the beetles are also in this fact sheet.