Detect Side Collision

side_collision.cs

void OnCollisionEnter2D(Collision2D col)
{
  if (col.gameObject.tag.Equals("Wall"))
  {    
    Vector3 hit = col.contacts[0].normal;
    Debug.Log(hit);
    float angle = Vector3.Angle(hit, Vector3.up);

    if (Mathf.Approximately(angle, 0))
    {
      //Down
      Debug.Log("Down");
    }
    if(Mathf.Approximately(angle, 180))
    {
      //Up
      Debug.Log("Up");
    }
    if(Mathf.Approximately(angle, 90)){
      // Sides
      Vector3 cross = Vector3.Cross(Vector3.forward, hit);
      if (cross.y > 0)
      { // left side of the player
        Debug.Log("Left");
      }
      else
      { // right side of the player
        Debug.Log("Right");
      }
    }
  }
}