Its a little more complicated than that. A players production on the floor is based not just on points scored but what events he is directly responsible for....in short you put a value on everything else in the game including points...for example if you take a shot it has a negative value if the you make a shot it has a positive value that is more than the negative value of missing it. If you get a steal it is worth positive points, rebounds worth points, turnovers are negative points, fouls negative points and on and on. When you add up the players positive points and subtract his negative points you get the players value. It isn't exact but it isn't solely based on points scored verses points against while he is in the game. There are different systems that use different variables and I am not sure which one ISU stat service uses. Number guys at colleges love this and so do most coaches. It is a headache trying to single handedly keep all the stats needed to plug into system to get the rating. For a sports writer to even try to do it while making notations about the game would be amazing...almost as amazing as our win last night!
Lets say player x steals the ball and gives it to player a and he passes to player b for a bucket. The score and noticable stat would be the points that player b put on the score board. It is what most fans pay attention to. Player x may not score a bucket and come out with a very strong +/- rating because of his defense...charges taken, defensive rebounds, steals, loose balls retrieved, tie ups,...all things that are positives yet are not directly responsible for points but they are directly responsible for team wins. Often these numbers are connected to the minutes played, not always though some systems are just production based. If you don't get into the game you are a zero. If you get into the game and have no effect, you are still a zero. If you're in the game a minute or twenty minutes and only get one rebound you have the same rating. Others systems would have a stronger value for production per minute played. To me the more games played the more it evens itself out no matter which way you do it.
