Can the Celtics have an elite defense?

Defense wins championships. That's the mantra that has been spouted for years, even as the league has shifted toward a more exciting brand of uptempo offense that thrives on ball movement and shooting. No matter how much the offensive side of the game changes, recent history shows us that defense is still a vital part of winning.

The reigning champion Golden State Warriors are led by MVP Stephen Curry, who is arguably one of the greatest shooters of this era, but not exactly known as a lock down defender. The Splash Brothers may steal the headlines for their barrage of long range shots, but what may go overlooked is that the Warriors were the league's best defensive team last season with a 98.2 defensive efficiency.

The last 9 NBA Champions have finished no lower than 7th in the league in defensive efficiency, while 9 of the last 13 have finished in the top 5. Sure, most of those teams had a superstar or two carrying them to the title, but not all of them. The 2003-04 Detroit Pistons were a collection of very good players, but none of them were considered to be among the top dozen in the league. Chauncey Billups led that team with an 18.66 PER, which ranked 43rd in the league. What that team did have was an elite defense that ranked second with a 78.7 defensive efficiency.

It's been well documented that this Boston Celtics team is lacking one of the league's top superstars, which pushes them out of the championship picture from the start in most people's minds. If they can't get a star this season then their best alternative seems to be having an elite defense.

Boston ranked only 12th in the league last season with a 102.1 defensive efficiency. That's not too bad, considering the increase in offense around the league over the last few years has taken a toll on defensive numbers. The Washington Wizards ranked 5th last year with a 100.0 defensive efficiency, so the Celtics aren't that far off. With some improvements this year, there is hope that Boston can become a top-5 defensive unit this season.

It starts on the perimeter. Boston boasts arguably the league's best defensive backcourt with Marcus Smart and Avery Bradley leading the way. Our own Kevin O'Connor discussed last month why Bradley can once again become an elite defender this season. Smart is also a tenacious on-ball defender who will only get better in his sophomore season. Smart was slowed by an ankle injury early last season, but he held opponents to 40.4% shooting from the field on shots he defended (DFG%) after the All-Star break.

Boston will also benefit from getting a full season from key contributors that they acquired mid-season last year. Jonas Jerebko held opponents he defended to 39.8% shooting last season, which was 4.6% lower than those shooters produced against other defenders (Diff%). Jae Crowder is another versatile defender that held opponents below their normal shooting percentage with a -1.0 Diff% last season. We also can't forget about Isaiah Thomas, who despite his size still managed to hold opponents he defended to 42.9% shooting, which was the best mark of any Celtics guard that finished the season with the team.

Where the Celtics are bound to struggle is protecting the paint. Boston ranked near the bottom of the league by allowing opponents to shoot 53.9% at the rim. The team lacks an intimidating presence that will make teams think twice about driving down the lane to challenge them and there are no real shot blocking threats on this roster. Tyler Zeller was Boston's best interior defender last season, allowing a 51.8 Opp FGP that ranked well outside the top-50 in the league. The addition of Amir Johnson will help, thanks to his high motor and relentless style of play, but the 52.3 Opp FGP he produced in Toronto last season was only a tick better than Jared Sullinger's (52.8). Not many were praising Sully for protecting the paint, so Johnson may only provide a modest upgrade.

Without a strong presence in the paint, it limits what the perimeter guards can do. It's no wonder that Bradley allowed a career-best 0.69 points per possession in his sophomore year, per Synergy Sports data provided to ESPN's Chris Forsberg. He was able to gamble more and hound opponents with relentless pressure knowing he had the ferocious Kevin Garnett behind him. This Celtics team doesn't have that luxury.

While the Celtics' interior defense could use some help, a strong perimeter defense will help keep opponents out of the paint to begin with. While the team may not have great one-on-one defenders in the paint, a strong help defense can help mitigate that concern. Brad Stevens is quickly asserting himself as one of the brightest young coaches in the league and will find ways to mask the team's deficiencies. Defense is about effort and there are few coaches that manage to get their players to work harder for them than Stevens.

The team that started the season in green last year was drastically different from the one the Celtics ended up with. It wasn't until after the break that the Celtics started to build some chemistry with their revamped roster and the results from the second half were encouraging. Boston posted a 100.3 defensive efficiency after the break that was tied for 8th in the league over that span.

This Celtics team should become a better defensive squad than the one that finished middle of the pack last year. There may not be quite enough here to put them at the top of the league, but they have the ability to challenge for a spot in the top-5. Climbing that high would put them in the conversation of being called elite, while history tells us that a defense of that caliber is worthy of being a contender.