The grey balls are an estimation from your scout as to how good that particular player is in comparison to the rest. Take note though that everyone's chart is different. Your player #48 (1 ball) could be someone else in the league's player #2 (5 balls). The reason that they're different is that the two different team's scouts heard different rumors about the player's skill. You find out how good the player *really* is compared to the rumors by scouting and interviewing the prospect. So it's kind of debated as to whether the grey balls actually mean anything.