It actually could be a number of things - a "whiff" of weed killer, wind or hail damage, etc., but you might compare it to oak anthracnose which has some similarities.
hortster

on the other hand.. the odds of any given tree having 100% perfect leaves.. is low to nil ...

after my week of 80's followed by 2 weeks of hard frost and freezes.. nearly every tree in my yard that has leafed out.. has similar damage.. to one extent or another ...

i am glad you are actually focusing closely on your tree ... they are very enjoyable..

but in all reality.. there is no reason to jump to disease or chemicals.. after some spring damage ...

now.. if it were the whole tree .. in its entirety .. then i might consider being proactive.. but isnt this one branch on a rather large tree??

ken

Ken, my arboreal friend, yes, it is one branch of a large, apparently healthy tree. However, freeze damage would have hit more than one branch. But, should it be the beginning of anthracnose or, more unlikely, oak wilt, the OP should be aware and search possiblilies. Neither you, I, or others here can accuately diagnose from those pix. I agree, no chems, no proactive jump! But, OP, keep thy eyes open.
hortster

I'm in Austin, TX... we can rule out freeze damage. We have had the worst drought in history followed with a relatively wet spring. Took a few samples to a good local nursery today. They suggested it might be some sort of root system disturbance - and this is a street tree planted in some serious clay soil. It could be that as the healthiest tree, it's roots hit a problem area first. A root barrier or something. If that's it, I'm probably going to see it in all the trees in a few years.

Also might be early stage fungal disease or early borer damage. Submitting pics to Ag Extension next...

I know it looks like the damage is localized to the leaves, but a shot of the lower half of the trunk may be helpful as well.

But, should it be the beginning of anthracnose or, more UNlikely, oak wilt, the OP should be aware and search possiblilies. Neither you, I, or others here can accurately diagnose from those pix. I agree, no chems, no proactive jump! But, OP, keep thy eyes open.
hortster

==>> exactly ... just keep your eyes peeled.. [what is the derivation of that phrase?? yuck]

talk to your county extension office.. you need LOCAL advice ...

at leaf out.. damage can be subtle.. and week old before it actually shows itself ... damage can even occur while still a bud .. and to rule out cold in toto .. or deny hot.. or drought... or anything else.. and jump to disease.. is not quite right in my book ...

early spring damage.. is hard to pinpoint.. for whatever reason .. but one should not jump to disease or sickness .. i guess that is all i am trying to say ...

ken