Spear shaft affects stamina damage

[MrMagolor]

Recently, I learned that the shaft of a spear has no effect. Now, having it affect the direct damage would make spears a little overpowered, so instead, how about making it affect stamina damage? 

It makes sense. A more solid spear would have better capability to knock your breath out of you and/or knock you down.

If you have a better idea, feel free to post it.