The rest of your plant looks health. It is possible that that branch was injured (environmentally) or by an insect and subsequently died.

I would prune all such yellowed leaf branches at the first sign. They serve no purpose but possibly a harbor for disease . Just to be on the safe side, I would spray it with fungicide.

I get the same thing on mine, here in S Calif.

I've been picking off the brown yellow leaves and I did spray with a copper spray.

In my case, I had no damaged branches, but upon "Close Inspection" it "seems" like it may be my cages that are causing the problem~~~~I first see the infected leaves that are touching some of the cages I used last year. I wonder if some kind of , kind of~~~~hmmmm , whatever clung on to the cages over our winter, and that's what's buggin my maters, (so to speak), alto it is not "Buggs") per say.

Next year I gonna use something to sterilize those cages as I don't see any of the brown yellow leaves where there are new cages.

I just thought that the cages sitting empty in the Sun would be enough to kill whatever was clinging to them, but "Apparently not".

Anyway, "so far so good" We are having the best tomato year ever, lots of nice big Tasty ones!!!

Gary

Here's another photo from an Early Girl plant. It's hard to see, but the two fruits just below have brown splotches covering their skin, and some brown raised patterns on one of them.

Here's a closer look at the brown splotches on the Early Girl fruit.