To protect archers:
"...the use of a pavaise, a head-to-toe shield, was often brought out as a semi-portable defense that the man could hide behind as he reloaded so that he would not be cut down by arrows, other crossbow bolts, or by charging horsemen. "

I remember the otherwise excellent movie made in 1945 by
Sir Lawrence Olivier. The writers didn't do their homework.
They showed the English archers climbing big trees to get
away from French cavalry. A description of the battle which
I read on Internet not long ago says the battle was fought
on a very large clearing shaped like a figure eight.
The French were in one lobe, the English in the there.
The constriction was made up of brush that hampered French
cavalry, but not the English archers. The other crucial thin
was that French crossbowmen had to reload by pressing their
weapon against the ground, and were in a muddly place. And
the English longbow could be fired much more rapidly.
The chevaux de frise did not come into use until much later.