Spartan spear mode (synergy between shield and spear)

I'd like to see synergy between shields and spears, so that if you activate the shield and spear while on the ground, the spear takes on a defensive position, creating a sort of thorny shield. And if you do this while mounted, the shield should reduce enemy damage by half, so that players using spears aren't so vulnerable.

I understand it can serve as a glass cannon weapon, but I feel the damage it does isn't enough to compensate for the lack of extra defense against enemies, especially creepers. This is even more critical if you can't have a horse readily available, like in caves.