Hitting an entity while sprinting (even invulnerable or during its invulnreability state) multiplies the horizontal velocity by 0.6. This also affects knockback, and can be abused to get less knockback, which is unintuitive. Known mechanic in 1.8 pvp, this still affects recent versions.

Step to reproduce:
1. Launch 1.16 and create a world
2. Set attackSpeed attribute to 24 or above (this step is not necessarily, only visual)
3. Summon a NoAI entity with Resistance V or above.
4. Summon a melee hostile entity, keep it from moving (using cobwebs or others) and get in survival mode
5. Get hurt by the hostile entity.
The knockback is normal
6. Spam click on the invulnerable entitiy
7. Get hurt while spam clicking AND sprinting.
The knockback is reduced by a power of 0.6