Executed by performing a "Shoryuken" motion (forward, downward then down-forward) and pressing kick, Alex launches himself in the air with his knee forward. If it connects with his opponent, the knee catches them in the chest. Both Alex and his opponent descend towards the ground with Alex keeping his knee on his opponent's chest, driving them into the ground.
This move is one of Alex's main anti-air attacks. Each version does the same, decent amount of damage. The startup and range of Alex's forward jump is determined by the strength of the kick button pressed. The Light version has the fastest startup, but travels the shortest distance. The Heavy version has the longest range, covering about 40% of the screen. However, it has the longest startup. The EX version has the same startup as the Light version, but inflicts slightly more damage than the other versions.
Alex can use this move as a combo ender. If he has his opponent in the corner, he can use his Crouching Heavy Punch to launch them in the air, allowing him to follow up with his with Air Knee Smash for a good chunk of damage. Unfortunately, this move is not a solid reactionary anti-air attack. Unless Alex gets a good read on his opponent's jumps and uses the Air Knee Smash early, Alex is better off using his standard, normal attacks for his anti-air options.
In addition, even if Alex does connect with this move, the recovery resets the neutral game. Alex thrives in being up close to his opponent, keeping them on their heels with frametrap normals and command grabs. If Alex hits his opponent with Air Knee Smash, he may have to work his way back in order to approach them and maintain offensive pressure.
The attack cannot connect with a grounded opponent, unless the EX Special version is used. In Street Fighter V, the opponent must be in the air in order for Alex to connect with this move. All versions of this move have a rather large hitbox and rely primarily on the hitbox to out prioritize aerial attacks rather than invincible frames. Moves with good hitboxes of their own, such as Urien's jumping HK etc can beat this move clean depending upon the angle of both moves. The Air Knee Smash (along with the Slash Elbow) is considered a secondary move for Alex and thus; unlike his signature moves, the Flash Chop or Power Bomb, it does comparatively low damage and needs EX meter to be effective. The EX version, however does inflict a good amount of Stun.
The non-EX versions of this move have a 'grab' hitbox. Hence they cannot be parried in the air. The EX version on the other hand has a small hitbox in front of it that can connect with grounded opponents. It has a minuscule amount of invincible frames on startup, thus can be used as a reversal uppercut. With timing, it can go through air-to-ground projectiles such as Akuma's Zanku Hadoken or Ibuki's Kunais. Functionally it can be seen as similar to Dan's Koryuken. The EX special version has a 'strike' hitbox and therefore can be parried on the ground or in the air.
- This move was likely inspired by the High Knee strike used by professional wrestlers Harley Race and Triple H.
- The biggest difference between the wrestling maneuver and the version Alex uses is that he follows them down to the ground after the initial strike, similar to another professional wrestling move called the Knee Drop.
- Alex does have the aforementioned high knee strike as his universal overhead (MP+MK) in Street Fighter III: 3rd Strike.