WALTHAM — Doc Rivers used to refer to the 16-year-old Jared Sullinger as the “fat, slow guy.”

The Celtics coach knew all about Sullinger’s game, even saw the 240-pound teenager haul in 27 rebounds once for his All-Ohio Red AAU team. Rivers’s son, Austin, played for Each 1 Teach 1, which Doc said lost to the Ohio Red in at least six national title games.