WALTHAM — Doc Rivers  has kept a close eye on Mike Longabardi for a long time.
When Thibodeau left after 2010, that left a void, one Rivers felt perfectly suited Longabardi. On Tuesday, during an open practice at the team’s training facility, Longabardi put on a show on just how to defensively coach up an NBA team consisting of stars who put defense first.
“Remember, every trap has to have a purpose,” the 39-year-old coach told his team at the beginning of a two-hour practice.
It’s just the kind of thing Rivers, who would occasionally chime in, wants to hear from his No. 1 defensive assistant.
“He’s been around it,” Rivers said after practice Tuesday. “He’s been in the office next to mine. He communicates it well. I just want him to be focused on that. Whoever is my defensive guy, that’s their only job. All the other coaches do everything, they help with the defense, they help with offense but whoever I make my defensive [assistant], that’s his job.”
Rivers said no one on the team took it harder when the Heat dropped 120 points on the Celtics in the opening night loss.
“I want him to take it personally when teams score,” Rivers said. “And he does. Trust me, the first two games, he wanted to jump off a bridge somewhere. And that’s what I want him to be. I want him to be mad at people and hold them accountable.
Before joining the Celtics for the 2007-08 season, Longabardi was with the Rockets for four seasons as an assistant coach/video coordinator for two seasons, the video coordinator for a season and the assistant video coordinator for a year.
Longabardi spent seven years as an assistant coach for the men’s basketball teams at Pfeiffer University, Adelphi University, Lafayette College, as well as Towson University. He was on the coaching staff that led the Lafayette Leopards to a Patriot League  title and an NCAA  Tournament berth. Longabardi also was a member of the coaching staff for the Celtics 2008 Championship team.