Constrained knockback - unity3d

Question

I have a playing field which is divided in 4 zones (as seen on the image below)
The player (blue) is on the second zone while there are 2 enemies (red) on the third zone. When the player throws an object and hits the enemy, the enemy is knockbacked in the next zone (4) but should stay within that zone.
If the enemy was being hit on the edge of the zone, I want him to still be in the zone 4 and not outside of it (if he got knocked back). I'm not sure if the direction of the hit matters in the calculation. The horizontal position (x) between the zone can be random, but should be constrained by the edges of the zone.
Question: When the enemy is hit, I want to calculate the knockback position while being constrained to the zone he will be knockbacked to.
Note that it can be on any shape of playing field (triangular, hexagonal, circular, ...)

Answer 1

New components
You can use the NavMesh systems to compute the next position of the enemy.
You can find those classes (Components) on github. They are official component, but still in development if I remember well, that's why they are on github.
Now, you can find many tutos over the internet showing you how to use those classes. Here is one good example, thanks to Brackeys.
How it will work
Once you have downloaded thoses classes, you will be able to do as the following
I created a very basic scene in which a wolf needs to go to the cross position (on right part of the image) but is not allowed to go on the lightest blue on the map (right part of the image, you can see a line in the middle). So the navs components will compute the closest point, as shown as the middle of a circle (left part). You can manually add an offset not to be exactly on the edge if you want.
You can find more informations here.
This method computes the closest point of a given position.
Compute the knockback position
Regarding your comments, to compute the knockback position, there is differents ways :
Axis-based position
If your scene is as simple as those rules :
Left to right is X axis
Top to bottom is Y axis
(or the opposite)
Then you can do as the following :
public Vector3 GetKnockbackPosition(Vector3 startPosition, float force)
{
Vector3 res = startPosition;
res.x -= force; // Could be Z axis, depends on orientation
return res;
}
Not axis-based position
You can do as the following :
public Vector3 GetKnockbackPosition(Transform transformToKnockback, float force)
{
Vector3 res = transformToKnockback.position;
res -= transformToKnockback.forward * force;
return res;
}
Here you have the forward which will help you. You can substract this value and add a force factor to control the knockback force.
So once you have computed the position, you can use SamplePosition to adjust it, whether or not it is inside a zone.
Tell me if something is not properly explained.