How to use OnCollisionEnter?

Questions & Answers
1

I’m don’t understand how it works. I want to use in if statement, when ball collision with player. How to use?

2

OnCollisionEnter is an event: Unity calls it when the object (which must have a Rigidbody) collides with any collider. This event may occur in both objects, the rigidbody and the hit object. In the player, the code could be like this:

void OnCollisionEnter(Collision col){
  if (col.gameObject.tag == "Ball"){
    // a rigidbody tagged as "Ball" hit the player
  }
}

In the ball, the code is pretty much the same - the only difference is that the col structure contains info about the object hit:

void OnCollisionEnter(Collision col){
  if (col.gameObject.tag == "Player"){
    // this rigidbody hit the player
  }
}

NOTE: Usually OnCollision events only occur when a Rigidbody hits a collider; when a simple collider (or CharacterController) hits a Rigidbody, this event will occur if and only if the Rigidbody isn’t sleeping - what means that it must be moving or spinning, since when the rigidbody properties velocity and angularVelocity fall below some limit the rigibody enters sleep mode.