WALTHAM — You could sense the urgency in his voice.
Doc Rivers  is a coach who exudes confidence and a positive attitude. But he also calls it the way he sees it and can push the emotional buttons of his players when need be.
After practice Saturday, he sent a very clear message to his second unit.
“They’ve got to get out of their [old] habits, wherever they’ve been,” Rivers said, referring clearly to Jeff Green , Sasha Pavlovic , Troy Murphy  and Nenad Krstic . “We don’t [practice] long but we play with intensity, play hard. You just see some of their habits and some of their habits have to change. It will. It’s just going to take time.”
Rivers made it clear before practice began with several hundred fans listening in that their “help” defense was very sub-par Friday night in a 107-103 win over the Warriors.
“Learning to cover for each other is number one,” Rivers said. “But you can’t do that unless you have unbelievable focus and intensity and that’s what we’re trying to show them. I thought they were trying to do the right stuff on their help [defense] but they were always late because they’re not ready.”
Then Rivers got really serious.
“A lot of pros practice and they think practice is leisure and we don’t believe that here. It’s quick here but it’s hard. When you have your starters, who are playing 35 minutes [a game] going hard and you have your second unit going in cruise control, that’s not going to settle well with me.”
During the open practice Saturday afternoon at their practice facility, which gave a peek to fans and special guests into some of their basic defensive principles, defensive coach Lawrence Frank  called out positions and assignments and helped Rivers get the new players accustomed to the Celtics ‘ way of defending.
“We talked about that before practice, just too much. When we switch, that means we’ve decided to take the easy way out, defensively. So that’s what we did [Friday] night,” said Rivers. “It’s funny, in the first half, we didn’t have a lot of switching. In the second half, I think we had 16 times where we switched. If we have two, that’s a lot for us so you could just see we decided to go through it. We won the game but that’s a dangerous way of playing.”
Another player will be added to the “new” mix of reserves when the team welcomes guard Carlos Arroyo  this weekend. The Boston Herald reported Saturday the Celtics agreed to terms on a pro-rated veteran minimum salary for the rest of the regular season; he will be eligible for the playoffs. The move was necessitated when guards Delonte West  and Von Wafer  went down with injuries in the last week
And while he was busy delivering messages loud and clear to the team, Rivers made it clear that he’s not about to burn out his starters just to win games and seal the No. 1 seed. So, reserves you BETTER be ready.
“We want [the top seed] but I’m not going to use our minutes to get it,” Rivers said. “I can tell you that. [Friday] night was because of the injuries in the middle of the game. Once we get healthy, our guys are playing lower minutes. We should be good enough to win the games, and that’s what we want to do.”