"Lately, we've been s----y," said Green.
Boston's defensive rating (points allowed per 100 possessions) is 109.2 over the past three games and 106.2 over the past seven. That's a noticeable jump from a season average of 102. The Celtics have allowed opponents three 100-plus-point games the past three outings, and opponents are averaging 100.3 points per contest over the past seven.
Even when the Celtics struggled amid a hectic November schedule, their defense was still a top-10 unit. Through Dec. 8, the team ranked ninth in the league with a defensive rating of 100.7 through 22 games. Entering Friday's action, Boston had slipped to 12th overall.
First-year coach Brad Stevens wasn't revealing any classified information when he noted Friday that practices the past two days have been geared toward the defensive side of the ball. And Green suggested the team went all the way back to square one in looking to get itself back on track.
"The past couple games, we've been giving up a lot of points, a lot of easy looks," said Green. "I think it was necessary for Coach to get us back to the basics. That's how we start our offense: by getting stops and getting out in transition."
It's a no-brainer that teams play better in wins than losses, but Boston's defensive splits between the two are pronounced. Boston's defensive rating in wins is 96.7, and it skyrockets to 105.8 in losses. Opponents average 92 points in Boston's wins versus 100.3 in the team's losses.
There's an obvious correlation between how Boston's offense performs when the team is generating stops as opposed to when the team is giving up points. It all goes hand in hand.
But for Stevens, it has to start on the defensive end. And the Celtics are determined to get back to the caliber of defense that served as the backbone of their most inspired play of the season.
How do they get there? Avery Bradley, an NBA All-Defensive second-teamer last season, said it starts with the intensity level on that side of the ball.
"Energy -- I mean, it's like night and day. When we come out and some games we're just all down in a stance, then some games it's like we're standing up, not really any energy at all," explained Bradley. "It's obvious when you watch film."
Stevens also seems to believe that the fix is largely mental. He has implored his team to recalibrate its focus level. The difference between Boston's eyesore of a rating the past seven games and being a top-10 defense is maybe two or three additional stops per game.
That doesn't sound like much over the course of a 95-possession game, but it goes a long way. And the key is being mentally locked into every defensive chance, which is probably more difficult than the physical aspect.
"I think everybody has to be better in what they do, just a little bit better at what they do," said Stevens. "We've got to be a little bit more consistent in what we do. Then hopefully you get the results you want."
In regards to the team's penchant to let up at times, Green noted, "I think [the defensive slippage is a] lack of focus, to be honest with you. That's all I can really say. I think our focus wasn't there all the way and I don't think we were locked in on the defensive end. I think we were more worried about offense at that point, myself included."
It's a vicious cycle. When the Celtics fret about their inconsistent offense, opponents capitalize and go on runs that Boston can't stop as the team puts even more pressure on itself to score. Boston's offense, particularly while waiting for Rajon Rondo to finish his rehab, simply isn't consistent enough to lean on.
Boston's success is predicated on the defensive end and using the momentum of multiple stops to generate points without being weighed down by a need to match the opposing team's output.
The Celtics emerge from a five-day break to host the Cleveland Cavaliers on Saturday afternoon at TD Garden. The Cavs have been one of the league's most inefficient offenses this season, but they have plenty of firepower and have seen a recent bump in offensive output (thanks in large part to Kyrie Irving's exploits). Boston scored one of its few lopsided wins this season over the Cavs, but Stevens has implored his team to bring the necessary focus on Saturday.
"If we don't play well, we'll get beat. It's pretty simple," said Stevens. "If we don't defend well, it's going to be really hard for us to win."
Computer simulations suggested the Celtics would own the worst defense in the league. When they lose focus, they resemble what the computer models expected. But when they play as a unit and with the defensive DNA injected by Stevens, the Celtics look like a legit top-tier defense.
For Boston, it's simple: In this court, the defense can never rest.