Concussion sidelines Celtics' Al Horford

Boston Celtics center Al Horford was declared out as a result of a blow to the head during practice that landed him in the NBA’s concussion protocol program.

Horford was hit in the head during Monday’s practice, was evaluated for a concussion and permitted to return. But when symptoms showed up on Tuesday, he was reexamined by team physicians and scratched from the lineup.

Horford is averaging 12 points, 5.3 rebounds and 4.7 assists per game.