I wrote the comparer method but it seems like it does nothing. (added * -1)

    static void Main(string[] args)
    {
        string currDirectory = Directory.GetCurrentDirectory();
        DirectoryInfo directory = new DirectoryInfo(currDirectory);
        var fileName = Path.Combine(directory.FullName, "players.json");
        var players = DeserializePlayers(fileName);
        var topTenPlayers = GetTopTenPlayers(players);

        foreach (var player in topTenPlayers)
        {
            Console.WriteLine("{0} : {1}", player.FirstName, player.PointPerGame);
        }

        fileName = Path.Combine(directory.FullName, "topten.json");
        SerializePlayersToFile(topTenPlayers, fileName);

        Console.ReadKey();
    }

    public static List<Player> DeserializePlayers(string fileName)
    {
        var players = new List<Player>();
        var serializer = new JsonSerializer();
        using (var reader = new StreamReader(fileName))
        using (var jsonReader = new JsonTextReader(reader))
        {
            players = serializer.Deserialize<List<Player>>(jsonReader);
        }

            return players;
    }

    public static List<Player> GetTopTenPlayers(List<Player> players)
    {
        var topTenPlayers = new List<Player>();
        players.Sort(new PlayerComparer());
        int counter = 0;

        foreach (var player in players)
        {
            topTenPlayers.Add(player);
            counter++;

            if (counter == 10)
                break;
        }

        return topTenPlayers;
    }

    public static void SerializePlayersToFile(List<Player> players, string fileName)
    {
        var serializer = new JsonSerializer();
        using (var writer = new StreamWriter(fileName))
        using (var jsonWriter = new JsonTextWriter(writer))
        {
            serializer.Serialize(jsonWriter, players);
        }
    }

}

public class PlayerComparer : IComparer<Player>
{
    public int Compare(Player x, Player y)
    {
        return x.PointPerGame.CompareTo(y.PointPerGame) * -1;
    }
}