Three flavors of "how much does this skater's positioning matter." Presence is the drop in team pitch control if you delete the skater entirely — bounded ≥ 0 by construction, so it measures "player exists," not "player positioned well." Δ vs centroid compares the skater's actual position to a "lazy replacement" who stands with teammates (velocity zero). Δ vs team is Δ vs centroid re-centered against the four teammates on the same frame (zero-sum, kills volume bias). Scored only when the skater is > 15 ft from the puck.