With three-quarters of the 2014-15 season complete, NHL.com looks at some of the biggest storylines and award contenders.

Kris Letang has developed a reputation for being an offensive defenseman, a player who can contribute on the score sheet from his position on the blue line. And lately, when it comes to awarding the distinction of best defenseman in the NHL, offense has been a major component of the conversation.

The past five Norris Trophy winners have finished either first or second among defensemen in scoring, three times leading defensemen in points (Duncan Keith in 2013-14, P.K. Subban in 2012-13, and Erik Karlsson in 2011-12). It's created some conversation about what criteria is and is not factoring into the voting.

Letang leads defensemen in scoring this season, but it's what he's added to his game at the other end of the ice, and how well-rounded it has become that makes him the Norris favorite at this point.

On a Pittsburgh Penguins team so regarded for its offensive prowess, Letang has been a rock defensively. His 55.6 shot attempts percentage (SAT%) is ninth among defensemen who have played at least 45 games entering Wednesday. On a good possession team (the Penguins are ninth in SAT%), Letang has a SAT% relative to the team's average (SAT%rel) of 5.5 according to war-on-ice.com, seventh-highest among defensemen who have played 45 games, meaning Pittsburgh is that much better when he is on the ice.

There are other metrics purporting a good defensive player that jump out in favor of Letang. The 27-year-old averages 25:40 per game, tied for seventh-highest among defensemen. Of those minutes, he averages 19 at even-strength, 2:50 shorthanded, and 3:48 on the power play. There are four defenseman in the League who average at least 19 minutes at even-strength, 2:30 shorthanded, and 3:00 on the power play: Letang, the Los Angeles Kings' Drew Doughty and the Nashville Predators tandem of Roman Josi and Shea Weber.

Letang though, unlike some players on that list and others in Norris contention, has limited scoring chances when he's on the ice in addition to driving possession to go along with his high usage. Letang has averaged 23.8 scoring chances against per 60 minutes, according to war-on-ice.com. Of defensemen who have played at least 700 minutes, Letang has the fourth-highest relative scoring chances-for percentage at 7.0.

Breaking this down, in all of the Penguins' even-strength minutes, they have a scoring chances-for percentage of 51.2. They average more scoring chances than their opponents do at even strength. When Letang is on the ice, that number increases by a significant margin, a direct correlation to Letang's ability to limit opportunities in his end and influence the game on the offensive side.

As much as many feel a player's offensive merit is only measured by how many points he produces (which Letang passes with flying colors), Letang has a goals-for percentage of 56.1 according to war-on-ice.com, meaning his team is scoring more at even strength when he's on the ice than it's being scored on.

By every standard, Letang is contributing significantly on the offensive and defensive ends, the true mark of a Norris candidate.

FINALISTS

P.K. Subban, Montreal Canadiens -- The Canadiens have struggled all season when it comes to shot suppression; it's what has made goalie Carey Price indispensable. Like Letang, Subban is beginning to shed the identity of an offensive defenseman who is weaker in his own end. His shot attempt numbers, though not sparkling, are very much negatively affected by his team's inability to drive possession. Subban has a SAT%rel of 6.7, second-highest among defensemen who have played at least 45 games. The Canadiens are a subpar possession team, with an overall shot attempts differential of minus-122. When Subban is off the ice that number dips to minus-156.

Though he's made strides in the defensive zone, Subban's production hasn't dipped. He's tied for second among defensemen with 48 points and is on pace to set career highs in goals, assists and points. He's fourth in the League in power-play goals and averaging more than 26 minutes per game (Subban has never averaged 25 minutes per game in the NHL). That's nearly three more minutes than he played per game when he won the Norris in 2013, and Subban is arguably playing better now than he did then. He's handling his increased workload quite well.

Drew Doughty, Los Angeles Kings -- Doughty is following up his incredible 2014 Stanley Cup Final run with quite the encore. He's second among defensemen in SAT% at 56.8, trailing only partner Jake Muzzin. Doughty is going to play more minutes than any skater this season; his current 1,854:13 of ice time dwarves Josi's second-place total of 1,727:14.

Usage doesn't always indicate a player's ability, but Doughty has navigated those tough minutes with a goals-for percentage of 54.8, according to war-on-ice.com. Doughty is 16th among defensemen in scoring but is getting fewer starts in the offensive zone, down to 32.8 percent from 34.7 and 34.9 his previous two seasons.

Also in the mix: Erik Karlsson, Ottawa Senators; Nick Leddy, New York Islanders; Duncan Keith, Chicago Blackhawks; Anton Stralman, Tampa Bay Lightning

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