is this Good Design? OOP Loose Couple Principle?

hello! i want to show you if my Design is "correct" according to OOP principles.

info :

• there is a ball which collects coins

• the ball is the player.

• there is a game manager

so before you see the Scripts i've made a graph :

i've made a Skill Class :

 using UnityEngine;
 using System.Collections;
 
 public class Skill {
 
     public int Duration { get; set; }
     SkillType Type;
 
 
 
     public enum SkillType
     {
         Unknown,
         Shield,
         Life,
     }
 
     //Constructor
     public Skill(int _duration,SkillType _type)
     {
         Duration = _duration;
         Type = _type;
     }
 
     public SkillType getType()
     {
        return Type;
     }
 }
 

then there is a coin prefab that has attached CoinSkill script on it

 using UnityEngine;
 using System.Collections;
 
 public class CoinSkill : MonoBehaviour {
 
     Skill ShieldSkill = new Skill(10, Skill.SkillType.Shield);
     GameCoreManager gameManager;
 
     // Use this for initialization
     void Start () {
         Destroy(gameObject, ShieldSkill.Duration);
         gameManager = GameObject.FindWithTag("GameController").GetComponent<GameCoreManager>();
     
     }
     
     void OnCollision2D(Collision2D collider)
     {
         if(collider.gameObject.tag == "Player")
         {
             gameManager.CollectCoin(ShieldSkill.getType(),collider.gameObject);
             Destroy(gameObject);
         }
     }
 
 }

& GameCoreManager script attached to GameManager Object

 using UnityEngine;
 using System.Collections;
 
 public class GameCoreManager : MonoBehaviour {
 
 
 
     public void CollectCoin(Skill.SkillType _type,GameObject player)
     {
         if(_type == Skill.SkillType.Shield)
         {
             player.GetComponent<SkillActivator>().ActivateSkill(_type);
         }
     }
 
 }

and finally the skillactivator script attached to player (ball) object

 using UnityEngine;
 using System.Collections;
 
 public class SkillActivator : MonoBehaviour {
 
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     public void ActivateSkill(Skill.SkillType _type)
     {
         if(_type == Skill.SkillType.Shield)
         {
             activateShieldSkill();
         }
     }
 
 
     public void activateShieldSkill()
     {
         //todo
     }
 }