Bats can walk, albeit clumsily. Their bodies are so highly adapted for flight that their legs serve mostly as attachment points for the surface of their wings. Crawling on the ground requires a lot of energy from bats because their leg bones are poorly designed for moving in that way.
Bat legs have knees that point outward and backward. This is an adaptation for crawling securely on cave walls and ceilings. It also allows the bat to control the shape of its wing surface if the bat has a membrane between its legs and tail. Most bats have very fragile leg bones that make for fumbling locomotion, but they can exert a great deal of force.
Although most bats are poor at walking on the ground, vampire bats are excellent walkers and are even known to sprint. They have somewhat thicker legs than most bats, though what difference this makes to locomotion is not known.