I think this is some kind of fungus which destroyed an insect. Not at all certain. Help appreciated.
Unfortunately, my photos are pretty bad. I was focused on other things on the leaf and didn't see this at the time. (Found it in leafhopper photos.)
Seen on what I think was American Sycamore (144455738), along with a lace bug (144455739), a beetle (144455741), aphids (144455742, 144455743), and leafhoppers (144455744, 144455745).