As the Blue team, your limited to much Slower yet Stronger classes. Your Goal is to protect the Hunted from dying. If he does, you'll need to respawn and try again. Because you can be multiple classes on Blue, each class has been split into it's own strategy. Basic strategy would be to stay close to the Hunted, and be aware of his location. Also be careful of spy's and remember the limited classes. If you see a spy as a Pyro, then surely he is a spy.
The Bodyguards team is limited to Soldiers, Medics, and Heavies. One player is The Hunted - an Engineer armed with only a wrench.
With the Red Team, you have much faster classes, yet classes that all have range attack issues. Your Goal is to kill the Hunted, or even clear a path just to get to him. In some cases, you may be able to find him, then skip the rest of the Bodyguards and rush the Hunted. If the Hunted dies, everyone is respawned and your team gets a point. Because both teams are respawned, in some cases this may allow the Hunted to get to a goal much faster then you. However remember half of his team is Fat, and slow.
The Assassin team is limited to Snipers, Spies, and Pyros. The Pyros have a limit on them so only a small amount may be played at a time.