These catch on grass and debris to prevent the arrow from being lost in the vegetation.
From the en.wikipedia.org
He suddenly catches sight of a carp swimming through the grass and in an instant he has drawn his bow and released the arrow.
From the al.com
However, Genghis Khan was wounded by an arrow on his knee in 1212 after the Mongols returned from their relaxation in the borderlands between grass and Gobi.