Feather both in fore and hind foot

A kind of dinosaur is said to have feather both in fore and hind foot. I saw that feature in a scientific book. I cannot imagine how they fly. I wonder whether they crawl on the ground. As I get older, dinosaurs become similar to birds. How do scientists explain the system of dinosaur getting the feather in hind foot? The recent bird's leg seems strange, which is very different from the feather. The vulnerability of its leg is similar to the hand of the Tyrannosaurus. Is there a strange connection between them?