Celtics' second unit finds success

The Boston Celtics have quietly wiggled back in front of the Chicago Bulls for the best defensive rating in the league, allowing 100.1 points per 100 possessions. So it should come as no surprise that its most heavily used lineup -- the Big Four and Glen Davis -- has benefited from that combo's emphasis on the defensive end and that four of those players -- everyone but Ray Allen -- are among the top 12 players in the league in defensive rating, according to Basketball Reference.

So what gives with Allen, who sits roughly four points behind the likes of Paul Pierce, Davis and Rajon Rondo? Well, playing heavy minutes with an inconsistent second unit this season has surely hurt his overall defensive rating.

Need an example? Allen's most common second-unit lineup (him and all reserves) this season featured him with Nate Robinson, Marquis Daniels, Glen Davis and Semih Erden. Over 56½ minutes this season, that unit gave up 128 points on exactly 100 possessions (for an easy-to-calculate defensive rating of 128).

How does that measure up? The league's average defensive rating is 107.2, according to Basketball Reference. What's more, the Toronto Raptors are last in the NBA with a defensive rating of 113.

Knowing the second unit hasn't been great at keeping opponents off the scoreboard, it was interesting to watch Celtics coach Doc Rivers sub in his reserves as the Philadelphia 76ers cut their deficit to four late in the third quarter Tuesday.

Boston not only pushed that lead back up to 10 before the end of the third quarter, but eyebrows shot skyward when Allen and a second-unit lineup featuring Davis, Delonte West, Jeff Green and Nenad Krstic held the 76ers scoreless over a four-minute, seven-possession stretch near the start of the fourth quarter, allowing Boston to extend its lead to 14 before the starters trickled back in.

Yes, the Celtics might have finally uncovered second-unit gold with a starter-light crew that can hold the fort while Boston's heavy hitters get extended rest (even at age 35, Allen seems able to play any amount of minutes). Kevin Garnett played only 24 minutes Tuesday, while starting center Jermaine O'Neal logged just 12:32.

"[The reserve unit] was huge for us," admitted Rivers. "And listen, we're getting healthier, so our bench is starting to resemble a bench. That's good."

That Allen/West/Green/Davis/Krstic lineup has shared the floor for roughly only 21.2 minutes, according to BasketballValue.com, but boasts a defensive rating of 88.2 during that span. And it's not as if the unit isn't producing offensively, as it boasts a sterling 109.4 offensive rating (a mark that would qualify Boston for top 10 in the league, if maintained).

So how did this happen? Green isn't regarded as the sort of lockdown defender Daniels was, and Krstic isn't exactly known for his defensive talents (not that Erden was either). Still, how exactly did Boston's second unit improve defensively by roughly 40 points per 100 possessions?

There's something to be said for the comfort level achieved in combining Green and Krstic, teammates in Oklahoma City. A healthy West and a sixth man of the year candidate like Davis add stability to that unit. But even the players were openly excited about the potential of that combination after Tuesday's win.

"I think we're getting together," said Krstic. "The first couple games when we played together, we were not on the same page, but I think the biggest key right now is that we're getting used to each other and playing together. I think that's the key for the second unit.

"I think, defensively, we were on the same page [Tuesday]. I think we played really good defense. Sometimes one guy is just late and the whole defense crashes, but [Tuesday] everybody was on the same page."

Green shared in his enthusiasm and pointed to Krstic's slide to a reserve role as a big reason for the uptick in play.

"It was good; great to finally get in a good rhythm for us," said Green. "For the future, it was good to get a good game under our belt, especially with the playoffs approaching, but it felt good for us to go out there and finally get some time to play.

"It's great having another big [in Krstic] to spread the floor. I've been with Nenad for a couple years now; I know what he can do. It's another big to play alongside of Baby and myself -- that's a big second unit."

And therein lies the biggest key. Even Rivers admits that Green is more suited for the small forward position, this despite the fact that he's been utilized nearly exclusively as a power forward during his career.

When forced to put Green at the 4, Rivers is trying to ensure that it's not against a bruising big like Elton Brand, noting that's not an ideal matchup. But put Green on your typical NBA swingman, and he can thrive by both blocking shots and rebounding.

After Rivers got on Green about his lackluster defense and low rebounding output, Green responded by blocking three shots and grabbing a team-high seven boards Tuesday.

The question moving forward is, as well as this unit has played in limited time, could Boston rely on a four-man reserve unit during the postseason? Rivers has said he'd prefer to leave two starters on the floor at all times to ensure no drop-off.

If the second unit produces the sort of offensive and defensive rating the five-man combo of Allen/West/Green/Davis/Krstic has produced, it's going to be hard for the starters to get back on the floor.

Chris Forsberg covers the Celtics for ESPNBoston.com.