Roman swords vs Greek swords

[Macedon]

No, if the opponent is coverd by his shield, and not giving you a target to stab, then
you go low and cut the tendons on the back of his legs.

You mean by kneeling down and then try to put your hand and sword around his leg keeping your shield above your head? Or do you keep your shield perpendicular to the ground? Sounds interesting. Isn't it dangerous? Doesn't it make you vulnerable too? I guess you have reenacted such a hit. Is something like that advocated by sources or reliefs?