Find out that player is not grounded

Questions & Answers
1

How can i find out that my player is actually not grounded? Is there any contrary of OnCollisonEnter?

Thanks for the answers.

2

If you are using a character controller you can use isGrounded

If you are not using a character controller you will have to create your own check as james_170482 pointed out.

“you could raycast down from the players feet…”(I suggest you ray cast from a point above the players feet so that you know for sure it will hit then subtract the height you cast the ray from. Compare the distance to a “maxheightbeforefalling” variable) "…and if it hits an object tagged ground for example get the hit point… "

The great thing about the raycast option is you have the ability to use layermasks with it. Maybe you have certain objects the player can fall through or certain objects you wish to ignore while checking “grounded”

3

Since you use 2D you could go for:

[SerializeField] private Layer ground;
[SerializeField] private Transform groundCheckPoint;

bool IsGrounded()
{
    Collider2D col = Physics2D.OverlapCircle(groundCheckPoint.position, 0.1f, ground);
    return (col != null);
}

The ground check point should be somewhere to the feet.