Players need a role in at least half their team's games and real volume: 15+ pass attempts a game for quarterbacks, 6+ carries and targets for backs, 3+ targets for receivers and tight ends.
Shares divide the player's season total by the team's season total over the same games (target share, air-yards share, carry share). WOPR = 1.5 × target share + 0.7 × air-yards share, the best single number for a receiver's opportunity. Weighted opportunities = carries + 2 × targets, since a target is worth more than a carry.
Efficiency stats (yards per carry, per target, per attempt, EPA) need a minimum number of chances before they mean much, so they show “—” until then. EPA is expected points added: how much each play moved the offense toward points.