History

Riot shields are lightweight protection devices deployed by police and some military organizations. Most are a clear polycarbonate, though some are constructed of light metals with a view hole. Riot shields are almost exclusively long enough to cover an average sized man from the top of the head to the knees. Some riot shields are designed to be bullet resistant against low velocity handgun and shotgun ammunition, but most are not. They are generally intended to be used in riot control, to protect the user from shrapnel, thrown projectiles, and splash from various weapons such as a Molotov cocktail.
 
Riot shields are used in almost every country with a standardised police force and are produced by many companies. Many riot shields are constructed from transparent high-impact plastic to enable the bearer to see incoming thrown objects, so the shield can quickly be positioned to deflect them away from the user's body.

Riot control tactics vary between different police and military forces the world over. Generally riot shields are intended to protect the user from thrown objects and projectiles and interlinked with others to form a physical barrier against rioters/protesters etc. However, they are also used to push protestors back, and in some cases can be used as short range weapons against threats to the shield bearer.
 
There have been cases of demonstrators imitating police shield tactics, as in the image on the right. The people in the image on the right have most likely divided road safety barrels, put handles on them, and covered the top edge with foam pipe insulators.

Singleplayer/Spec-Ops

The Riot Shield only breaks in Survival Mode (not in Multiplayer) after enough damage is dealt to it and can only be fixed by switching to another riot shield or buying a new one. Bashing enemies with the riot shield is more effective than knifing them, as 200 points enemies get killed by one bash, while with the knife it takes 2 hits.

Additionally, friendly NPCs wielding Riot Shields can be called in to assist the player(s).

Multiplayer

 Th Riot Shield is availible to use in place of your Primary Weapon. 

It's also seen as a usable weapon in Multiplayer, and when the Juggernaut streak is achieved, the player will be automatically granted a Riot Shield and a USP.45. In multiplayer it can also be equipped with a weapon proficiency, Melee or Speed. It will be filled with cracks if enough damage is absorbed but will never break in Multiplayer.

Challenges