Unet: Add a force to hit player (by projectile)

I am trying to add an explosion force to a player object by the projectile that hit him. Any suggestions on how to achieve that? It works for some rigidbodys spawned by Network.Spawn() but not for the player object.

I use this code for the Projectile:

 using UnityEngine;
 using UnityEngine.Networking;
 
 public class ShellExplosion : NetworkBehaviour
 {
     //public GameObject explosionEffect;         
     [SerializeField]
     private ParticleSystem explosionEffect;
     public float maxDamage = 100f;                    
     public float explosionForce = 1000f;             
     public float maxLifeTime = 10f;                 
     public float explosionRadius = 5f;               
 
 
     private void Start()
     {
         // If it isn't destroyed by then, destroy the shell after it's lifetime.
         Destroy(gameObject, maxLifeTime);
     }
 
 
     private void OnTriggerEnter(Collider other)
     {
         Collider[] colliders = Physics.OverlapSphere(transform.position, explosionRadius);
 
         // Go through all the colliders...
         for (int i = 0; i < colliders.Length; i++)
         {
             // ... and find their rigidbody.
             Rigidbody targetRigidbody = colliders[i].GetComponent<Rigidbody>();
 
             // If they don't have a rigidbody, go on to the next collider.
             if (!targetRigidbody)
                 continue;
 
             // Add an explosion force.
             targetRigidbody.AddExplosionForce(explosionForce, transform.position, explosionRadius);
         }
         // Unparent the particles from the shell.
         explosionEffect.transform.parent = null;
 
         // Play the particle system.
         explosionEffect.Play();
 
         // Once the particles have finished, destroy the gameobject they are on.
         Destroy(explosionEffect.gameObject, explosionEffect.duration);
 
         // Destroy the shell.
         Destroy(gameObject);
     }
 }

I could spawn the projectile with client authority but i dont know if thats a good way to do it. As it is spawned by Network.Spawn() it should be doing the AddExplosionForce on the server, right? And as i mentioned, it is working for some cubes i spawned in for testing.