title: How to detect whether a player drops below a certain Y level
body: <p>I'm trying to write bukkit plugin and one of the features I would like to add is when a player drops to Y level 8 or lower it runs a command on that player. My current case is I'd like to teleport them to other coordinates if they drop to Y level 8 or lower.</p>
  
  <p>Is there a lite way of doing this without have a command run on every "move" event getting each players location then getting their y position then checking if it's less than 9? cause that seems like it would be a lot of work on the server if there are many people moving around. </p>