This is the hardest hitting attack in the Protection warrior's arsenal, so use it whenever you can. You generate more threat per point of rage with this ability than with [Devastate]. The ability offers a good solid chunk of (potentially critical) damage, which is independent of equipped weapon stats, and can even be delivered while disarmed, if need be.
Shield Slam is an epic Warrior spell in Hearthstone. The flavor text reads: ""What is a better weapon? The sharp one your enemies expect, or the blunt one they ignore?" - The Art of Warrior, Chapter 9"
Patches and hotfixes
Patch 9.0.1(2020-10-13): Level reduced to 3, Now available to all specializations, no longer generates Rage or resets cooldown by default. Rank 2 (Protection Level 10) re-adds Rage generation (now generates 15 Rage, down from 20), Rank 3 (Protection Level 28) re-adds cooldown reset (with addition of [Execute], Rank 4 (Protection Level 44) increases its damage by 20%.
Patch 5.3.0(2013-05-21): Now receives a 50% bonus to attack damage from attack power (down from 100%) for Warriors below level 85.
Hotfix (2013-03-12):Shield Slam now deals 25% more damage.
Patch 5.2.0(2013-03-05): The base damage has been increased by 150%, but now scale approximately 10% less efficiently with attack power.
Patch 5.0.4(2012-08-28): Can now be used in any stance and cost no Rage, generating 15 Rage if used in Defensive Stance. No longer dispels magic effects.
Hotfix (2010-11-23):Shield Slam's damage has been reduced by about 28% at level 15, with less, but still noticeable reductions at higher levels.
Patch 4.0.3a(2010-11-23): Contribution of attack power reduced to 60%, down from 75%, and base damage brought up so that a level 85 warrior in Heroic dungeon gear deals the same damage with no Vengeance, but Vengeance has less impact. In addition, Shield Slam no longer generates 30% bonus threat from its damage.
Patch 4.0.1(2010-10-12): Now the level 10 Protection Specialization ability. The damage is now based on Attack Power.
Patch 3.3.2(2010-02-01): The damage scaling from block value for this ability now diminishes faster and diminishes starting at a lower block value. The difference should be negligible for players in high-end tanking armor. In addition, the threat caused by Shield Slam has been increased by 30%.
Patch 3.2.0(2009-08-04): The benefit from additional block value this ability gains is now subject to diminishing returns. Diminishing returns occur once block value exceeds 30 times the player's level and caps the maximum damage benefit from shield block value at 34.5 times the player's level.
Patch 3.0.2(2008-10-14): Shield Slam is now available to all warriors, starting at level 40 and damage slightly increased.
Patch 2.3.0(2007-11-13): Shield Slam now always tries to dispel one Magic effect on the target.
Patch 2.1.0(2007-05-22): Rank 3 of this ability no longer gets its cost reduced twice by the [Focused Rage] talent (Protection).
Patch 1.12.0(2006-08-22): This ability will sometimes no longer remove more than one beneficial effect from the target.