HostData.connectedPlayers  

// Requests info from the master server and prints
// the number of players playing on each host

function Start() {
    var hostData : HostData[] = MasterServer.PollHostList();
    for(var element : HostData in hostData) {
        Debug.Log(element.connectedPlayers + " are connected to " + element.gameName);
    }
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Start() {
        HostData[] hostData = MasterServer.PollHostList();
        foreach (HostData element in hostData) {
            Debug.Log(element.connectedPlayers + " are connected to " + element.gameName);
        }
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Start():
        hostData as (HostData) = MasterServer.PollHostList()
        for element as HostData in hostData:
            Debug.Log(((element.connectedPlayers + ' are connected to ') + element.gameName))