Still wondering if not for hamstringing, perhaps for cutting the saddle strap to unhorse your opponent? Or snagging his clothes/knocking him from the saddle. Hey, it would allow the Spanish to try and capture the horse during the fray.
And speaking of weapons/tools with an odd purpose (to show that sleeve catchers and saddle straps cutters aren't impossible)-
https://en.wikipedia.org/wiki/Tsukub%C5%8D