title: BeautifulSoup returns None even though the element exists
body: <p>I have gone through most of the solutions for similar issues but haven't found one that works and more importantly haven't found an explanation of why this occurs outside of when Javascript or something else is being called on the site being scraped.</p>
  
  <p>I am trying to scrape the table for game "Officials" from the site:
  <a href="http://www.pro-football-reference.com/boxscores/201309050den.htm" rel="noreferrer">http://www.pro-football-reference.com/boxscores/201309050den.htm</a></p>
  
  <p>my code is:</p>
  
  <pre><code>url = "http://www.pro-football-reference.com/boxscores/201309050den.htm"
  html = urlopen(url)    
  bsObj = BeautifulSoup(html, "lxml")
  officials = bsObj.findAll("table",{"id":"officials"})
  
  for entry in officials:
      print(str(entry))
  </code></pre>
  
  <p>I am just printing to the console for now, but I get an empty list with findAll or None with find.
  I have also tried this with the basic html.parser with no luck.</p>
  
  <p>Can someone with a better understanding of html educate me on what is different about this webpage specifically?  Thanks in advance!</p>