A Backstab is a classic RPG attack type found in Dragon Age. The Backstab is a Rogue-only ability that does the same attack damage as a Critical Hit without being counted as a Critical Hit.
The information from this wiki article is drawn from the forum thread on Small Shields and Backstabs and all credit goes to the members posting in that thread.
 How it Works
Each enemy has a red circle, with a black bit in the opposite direction to where they're facing. If you attack them from this angle then your attack is an automatica Backstab which deals more damage.
Here are a few points of interest:
- A Backstab always inflicts the same damage as a Critical Hit.
- A Backstab is not a Critical Hit. It does Critical Damage (+50% damage), but is not considered a Critical Hit by the game, so it will not shatter frozen or paralyzed foes.
- Backstabs work with any Melee weapon, including Two-handers if you're inclined to use them. However, as Rogues don't have any Two-Handed talents, you'll simply be auto-attacking if you decide to use them.
- Backstabs cannot Crit.
 Increasing Damage from Backstabs
There are several ways to increase the damage done by a Backstab. The most commonly used are Lethality (use Cunning instead of Strength to determine Combat Damage, but only if Cunning is higher than Strength), Exploit Weakness (Assassin ability that gives bonus damage to Backstabs based on Cunning), and The Tainted Blade (Warden's Keep DLC ability that adds bonus damage to all attacks based on Cunning, but inflicts a steady 10 points of damage every 3 seconds). Rogues using Backstabbing tend to favor the Cunning stat over any other.
 Dual Wielding and Backstabs
When Dual Wielding, the game has a few quirks on Backstabs. Here are a few things to note:
- The game alternates which weapon it uses to determine combat damage every few seconds. If you're using a full-sized weapon and a dagger, your damage will go up and down every few seconds. However, the game does not change the animation; it appears as if only the Main Hand weapon is being used.
- Any damage runes on the Main Hand weapon are applied at all times, even when the game is using the Off Hand weapon to determine damage. This means that any Damage runes on the Off Hand weapon are wasted; however, Dweomer and Hale Runes are still effective in your Off Hand weapon.
 Small Shields and Backstabs
There is some discussion in the Dragon Age Forum regarding backstabs and dual wields vs backstabs with small shields. In particular, member constantplanck has this to say:
I had wondered the same thing at first but once my rogue learned how to go stealthy in combat and I expanded the backstab range I realized that my second weapon was serving absolutely no purpose...you don't use it for backstabbing and since the backstab is an automatic crit there's no reason to use any attack pattern other than stealth/stab/dirty fighting/stab/stab/stab. Especially if you're playing a ranger build and your animal companion can always draw aggro.