In vanilla Skyrim...
even after maxing out your blocking skill and acquiring all perks, blocking with a shield still damages your health.
This is immersion breaking.

blocking as a low level character hurts a great chunk of your health.
This makes blocking in early game pointless.

shielded enemies(especially guards) always have their shields raised whenever you try to land a hit.
This makes battle against them annoying.

-<|Core Features|>-

Stamina blocking: blocking now costs stamina only. As long as you block a hit and have enough stamina to take all the damage, you receive no health damage.

Guard break(optional): when stamina is less than enough to block an incoming hit, you(or NPCs) take the portion of damage that's not covered by stamina, and optionally stagger. Just like Dark Souls.

No Regen on Blocking(optional): when blocking, stamina does not regenerate. This is to balance NPCs that always have their shield raised.

Configuration: Stamina consumption can be tweaked in .ini with separate multipliers for weapon/shield stamina costs & player/NPC stamina costs.
Stamina cost does not follow your difficulty settings. That means if you're playing at higher difficulties that x3 your received damage and x0.5 your damage output, you may want to x3 the stamina damage mult for player and x0.5 for NPC for better consistency. I'm not synchronizing them because I want to give players more freedom.

Script-free: Everything is handled through a few lines of simple SKSE codes. There will be no script lag and you can safely install and uninstall it on an existing save as you wish. 

-<|Compatibility|>-

Unlike in Reliable Blocking,  blocking efficiency is affected by your perks and magic effects, and your skill level increases as you block. 
This makes this mod compatible with all perk and magic overhauls: Ordinator, Vokrii, Adamant, Perma, SPERG, Requiem, Sexlab, Osex, etc... are all compatible. 

Unlike Vigor that utilizes a clever workaround to achieve stamina blocking(recovering the health damage instantly on blocked hit and transferring the damage to stamina), SOS does its calculation at the very moment when health damage is applied onto the blocker. This means you won't get killed when blocking with enough stamina at super low health. 

In addition, this mod is compatible with all major combat overhauls as well as perfect-blocking mods: Ultimate Combat, Wildcat, Smilodon, Blade and Blunt, Deflection, Hellblade timed block, Inpa Sekiro Combat, Schlongs of Skyrim, CBBE, SAM, etc... are all compatible as well.

This mod does not work with Legendary Edition, and I do not plan to port it myself. However feel free to port it and publish it as a separate mod if you want.

Github

-<|Credits|>-

• SKSE team for SKSE.
• Fudgyduff for Clib.
• DropKicker for DKUtil.
• Dydaus for Reliable Blocking that inspired this plugin.
• Loki for the hook from Stagger on Hit.
• 绝伦少年 for making the cover image.
• xtmt for porting the plugin to AE.
• People of Cowboy Bebop discord for testing. 
  

-<|Wall of Shame|>-

The following individuals are strictly forbidden to include this mod in their modpacks :
原子 
(for selling Lexy's LOTD modlist for 40$ per copy and branding it as their exclusive modpack)
旋旋 
(for selling paid Skyrim modpacks and branding Dyndolod 3.0's distant grass lod as its exclusive feature)
沙耶 
(for selling paid Skyrim modpacks)