Former Celtics forward Walter McCarty will rejoin the team as an assistant coach a league source confirmed to the Globe Tuesday night. With the addition of McCarty a 6-foot-10-inch forward who played for the Celtics from 1997 to 2005 to new head coach Brad Stevens's staff Stevens who has no NBA experience gains the valuable perspective of an ex-NBA player that should help ease Stevens's transition into the league. McCarty is also a product of the Kentucky Wildcats as is Celtics point guard Rajon Rondo. A league source had previously told the Globe that the Celtics were looking to add a staff member "who can bond with Rondo someone he can relate to and trust." McCarty spent three seasons as an assistant coach to Louisville coach Rick Pitino a former Celtics president and coach who coached McCarty at Kentucky. McCarty also served as an assistant under former Indiana coach Jim O'Brien who coached McCarty in Boston.