I've got about a dozen tomato plants of different varieties in containers on my northeast-facing deck (mid-Atlantic region of the US), which receives about 6 hours of direct sun exposure per day. Some of them have developed these black splotches on their leaves. Based on these articles on Southern Living and Old Farmer's Almanac, it looks like this might be a sign of Septoria leaf spot. Is that what this looks like to you all as well?
EDIT: Clarified orientation and daily sun exposure.
Definitely not septoria; septoria usually starts in the lower leaves, has a more spotty pattern to it, and kills leaves as it moves along the plant.
What you’re showing looks more like mechanical damage, probably from wind banging the leaves against that rung of the cage, or possibly a cold snap if you’re somewhere far north. Sunburn would usually be on the list of possibilities too, but not likely per your description.
This particular plant has been through some hard times. Before I had staked it, the top part of the main stem that had outgrown the cage got bent in half when a nasty thunderstorm blew through. This leaf is "below" the point of injury; that said, if you look in the top left corner of the photo, you can see where it happened and where the plant kinda healed itself, but everything from that point up toward the growth tip of that stem looks extremely sad like it never fully recovered.