I am trying to make a Hunger Games map on MC 1.5.2 and I am almost finished. I have most of the command blocks set ready for the games but for some reason, everyone keeps spawning on top the glass sphere and not in the lobby I made. Even after I changed the spawnpoint and did /kill, I still spawned on top of the sphere so to counteract that, I made a TP command block which TPs all people to the lobby. Though what I want is something that can TP each person to the lobby when they join, automatically, so that they don't spawn on top the sphere without them being able to get to the lobby and having me to manually press the TP all to lobby button.

So, any suggestions on how I can make an Auto-TP when people join my server?