"Usage Percentage" is an estimate of team plays used by a particular player when he's on the floor - players with high rates are usually those you want touching the ball in scoring position whenever possible.
Usg% - Usage Percentage (available since the 1977-78 season in the NBA); the formula is 100 * ((FGA + 0.44 * FTA + TOV) * (Tm MP / 5)) / (MP * (Tm FGA + 0.44 * Tm FTA + Tm TOV)).
AST% - Assist Percentage (available since the 1964-65 season in the NBA); the formula is 100 * AST / (((MP / (Tm MP / 5)) * Tm FG) - FG). Assist percentage is an estimate of the percentage of teammate field goals a player assisted while he was on the floor.
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