Knockback is how far you fly from an attack in the Smash Bros games. Some attacks have high knockback such as Bowser's side smash or the Greap's attacks. Standard attacks usually have low knockback. The higher your damage percent is the farther you will fly from an attack and also the attack will have more knockback than usual. Also depending on the difficulty level you are playing on the higher knockback you will get when attacked. So if you played on intense difficulty and you got hit by a powerful attack you can be sent flying. Final Smashes have high kncokback and usually KO. Bumpers and Flippers have high knockback. Damage ratio also has an effect on knockback. On 0.5 you attacks don't have high knockback while on 2.0 attacks (even standard attacks) have high knockback.