Basic Attack

Basic Attacks (also called AA - Auto Attack) are the attacks that a Hero, Minion, Mercenary, Monster, Summon or Structure will perform automatically, if they are capable of hitting the target. Players can cause the units they are controlling to perform a Basic Attack by pressing the Right Mouse Button on an enemy unit. Most units' Basic Attacks deal Physical Damage almost exclusively, except in some circumstances. As an exception, Non-heroic Summons' Basic Attacks deal Spell damage. Floating damage text displays the damage dealt by physical attacks as orange numbers above the target's head. Damage from Physical Basic Attacks can be reduced by applying Armor, Physical Armor or Parry on the target or any physical and all-damage attack debuffs on the attacker. Blind is a debuff that causes the affected units miss their Basic Attacks for a set period of time, and Heroes with Evasion cannot be hit by Basic Attacks.

Some Heroes are designed around their ability to do damage through Basic Attacks so have higher Base damage or Attack Speed. Heroes like Raynor or Sgt Hammer utilize their Basic Attacks for the majority of their damage, and Heroes like Illidan or The Butcher require their Basic Attacks hitting to survive due to their heavy reliance on attack Lifesteal. Other Heroes (typically mages or supports) do very little auto attack damage because their kit may provide utility elsewhere, or their damage might simply be based on their Abilities instead.

Attack Damage
The Base damage statistic determines the damage a unit does when they attack an enemy with their Basic Attack. All heroes start with a Base attack damage value that increases with Scaling, and certain abilities or talents (such as Follow Through) can also increase attack damage under certain circumstances. A couple heroes such as Li-Ming, Kel'thuzad, and Kael'thas can make their Basic Attacks deal Spell damage instead through certain talent selections.

Attack Speed
Main article: Attack Speed

Attack Speed (not to be confused with the speed of the attack projectile) is the rate at which a unit can use their Basic Attack. Attack Speed is measured in attacks per second, so higher Attack Speed values mean more attacks per second and lower Attack Speed values mean the opposite. The combination of Attack Speed and Attack damage multiply together to show a Hero's damage per second (dps), and many Basic Attack focused Heroes utilize having a high dps to kill their enemies. Some Talents and Abilities can increase Attack Speed, while other talents like Imposing Presence can greatly reduce it.

Attack Range
Main article: Range

Each unit has a certain range that targets must be within to be able to attack them, measured from the edge of the attacking unit's hitbox to the edge of the target's hitbox. If a Hero wishes to attack someone outside of their range they will first have to move closer to be able to target them. The attack range of a hero also determines whether they are melee or ranged, with ranged Heroes having longer range but generally utilizing projectiles, and melee Heroes having short range but their hits landing instantly.

Stutter-stepping
Stutter-stepping is a vital technique for Basic Attack driven Heroes that involves rapidly moving between each Basic Attack's "cooldown" to maximize mobility without losing overall damage per second. Stutter-stepping can be used to cover distance while chasing the target to prevent target getting out of your Range, or to make your Hero a moving target to make it harder to aim skillshots at it. The effectiveness of stutter-stepping is very reliant of the Hero's Attack Speed. Heroes with high Attack Speed, like Zarya and Tychus, have only a little time between attacks to move, causing them to lose dps by trying to stutter-step, so they are usually required to stop attacking completely and reposition. However, this is a non-issue for Heroes who can attack while moving, like Tracer, Lucio or D.Va, or Heroes with slow Attack Speed, like Leoric, that can cover more ground between the attacks and are less likely to lose dps because of it.

Trivia
Blizzard tried multiple times (with Probius and Junkrat) to create a Hero without Basic Attacks:


 * We've tried doing Heroes with no BA a couple of times now, and it always ends up feeling awkward. You can't kill Scouting Drones, Blackheart's treasure chests become exceptionally difficult to open... But most importantly, it feels bad when you need to do that last little bit of damage (ex: Minion with a sliver of HP) to something and have to waste an ability CD/resource to do it. This holds true even for Heroes with relatively short CDs and few or no resource constraints.
 * For Junkrat, we stuck with the Melee BA for a while, but the rate at which we had to let him spam his Q in order for that to feel OK made him exhausting to play against - Grenade dodging fatigue was a real thing when he could shoot them almost constantly. His Q being so spammy also took away most of the decision making from using it. Increasing the CD on Q charges and filling the gap with a Ranged BA made him more engaging to play both as and against.