When Sarthak Malani passes other runners in a half-marathon, the astonished look on their faces gives him a little ping of satisfaction. 

Mr. Malani has a clear view of those faces. He runs backward.

“People are always telling me I’m going the wrong way,” Mr. Malani said.

If so, he isn’t the only one. More runners these days are reversing direction, even on treadmills—turning around and running where they can’t see ahead. What could possibly go wrong?

Some are running backward to fight boredom, some to challenge their coordination and balance, and some, as in Mr. Malani’s case, in hopes of rehabbing an injury.