Really? So by your logic "100 possessions" means one game? Do both teams clear the floor once that happens? Is the game over?
You don't know the term "per 100 possessions".It's a benchmark,measurement number, that can be used as a basis, to measure a players value on both ends of the court.
A key tenet for many modern basketball analysts is that basketball is best evaluated at the level of possessions. During a single game, both teams have approximately the same number of possessions, because they alternate possession. (A team can have slightly more if it begins and ends a quarter or half with possession.) However, over the course of the season, teams play at very different paces, which can dramatically color their points scored and points allowed per game. Therefore, these analysts favor use of points scored per 100 possessions (Offensive Rating) and points allowed per 100 possessions (Defensive Rating).
Or see here: http://basketballvalue.com/teamplayers. ... =2009-2010
for a more thorough,detailed meaning of "per 100 possessions".