test.cs

using UnityEngine;
using System.Collections;
using UnityEngine.Networking;
using System.Collections.Generic;
using System.Linq;

public class Test : NetworkBehaviour {
    public bool isReady
    {
        get
        {
            List<NetworkConnection> connections = NetworkServer.connections.FindAll(c => c != null).ToList();
            NetworkConnection hostConnection = NetworkServer.localConnections.Find(c => c.isReady && c.hostId == -1);

            if (hostConnection != null && connections.All(c => c.isReady))
                return true;
            return false;
        }
    }
    public bool isRunningGame { get; private set; }

    void Start () {

    }

    void Update()
    {
        if (!isRunningGame && isServer)
        {
            if (isReady)
            {
                RpcStartGame();
            }
        }
    }

    [ClientRpc]
    public void RpcStartGame()
    {
        isRunningGame = true;
    }
}