Subterfuge, tactics, and maneuver are key elements in any engagement. Often one side is caught off guard and must flee rather than be defeated. In other instances a successful maneuver is countered immediately by the opposition and forces have to be withdrawn thier real mission already complete. Few conflicts are totally equal and any out numbered force must choose the time and location of every engagement or risk quick destruction. In escape plots one side must leave the field while taking as few casualties as possible. Often the fleeing force is cut off from thier line of retreat or even surrounded.
 

1-10    After crash landing on an isolated world survivors must flee hostile
           aliens/natives as they try to reach a distant outpost or transmitter.

11-20   An assassin has just eliminated his target (an enemy leader, etc.),
           and now must effect his escape from the city.  Angry citizens and
           vengeful security forces will stop at nothing to prevent his escape.