The three in front are old and sick, they walk in front to set the pace of the running group lest they get left behind.
The next five are the strongest and best, they are tasked to protect the front side if there is an attack.
The pack in the middle are always protected from any attack.
The five behind them are also among the strongest and best; they are tasked to protect the back side if there is an attack.
The last one is the LEADER. He ensures that no one is left behind. He keeps ready to run in any direction to protect and serves as the 'bodyguard' to the entire group.
Just in case anyone wanted to know what it really means to be a leader. It's not about being out front. It means taking care of the team.