Greaves are armor for the shins. In the early 14th Century, some of the richest knights had steel greaves, but many greaves were of leather, which might have been boiled for hardness or strengthened with metal studs or splints.
My greaves are splinted leather, with metal strips riveted into them. At the knee, they are tied onto the gamboised cuisses with points and laces.
This image from the funeral brass of Sir Miles de Stapleton, dated 1364, shows splinted greaves and cuisses. The plates for the thighs appear to be inside, and the plates for the shins appear to be outside. Both of mine are on the inside.