This is a plastic guard to stop bricks and other debris from falling onto passers-by.

It is fitted to the sides of scaffolding walkways and is a safety requirement. These guards have folding hooks that allow easy attachment to the scaffold poles at the top, and the kick boards at the bottom, but also allows them to stack flat. Traditional plastic brick guards each have to be zip tied in at least 4 places which is fiddly and time consuming. 

They also clip together to form a continuous run along the length of the walkway.