Birdirbir

One player bends over with hands on knees to form the first "back."

The next player runs up and leapfrogs over the bent player, then bends down further along to form a new back.

Each following player leapfrogs over every back in line before adding their own back at the end.

The line of backs grows longer each round, making the leapfrog course longer for later players.

Anyone who touches a back without clearing it, or refuses their turn, takes over as a back themselves.