Celtics Tap Sam Cassell as Top Assistant Under Joe Mazzulla

Sam Cassell is joining the Boston Celtics' coaching staff.
Cassell spent the last few seasons with the Philadelphia 76ers.
Cassell is returning to Boston, where he won a championship in 2008.
Cassell has experience as an NBA player and coach.
The Celtics lacked experience on their staff for much of last season before adding Cassell.