This spring near me was so odd what with early warmth and late freezes that many trees and plants still show the damage. Things that have always done well in the past look ragged.

Could that be what happened to yours?
A late freeze could have done what you are describing.

It doesn't look like frost damage. The leaves are just all small and stunted, with no new growth at a time when it's usually growing like mad.

We did have a wet cool spring but I thought that would be good!

Would a rootbound tree do this? I had a crab die on me, and when we dug it up there were nice radial roots at the top but the rest of the roots were bound up below.

Yes rootbound can do what you are seeing. But so can root damage if it is not draining properly. You mention clay soil, which in and of itself is not a bad thing. But clay soil that water does not move through is bad news.

Post to the "trees" forum with some pictures. There are lots more people there with allot of experience.

Arktrees