(Kris Russell battles for positiong with former Bruin Reilly Smith during a Bruins-Flames game in March 2015. Photo by Joe Makarski, Bruins Daily)

Four days after signing center David Backes to a five-year $30 million deal, the Hub of Hockey is still scratching their heads about not only that move for a 32-year-old but also why no Bruins’ splash for help on the blue-line.

No question Backes, the former long-time Blues leader and recent captain, deepens Boston’s depth in the pivot roles with Patrice Bergeron, David Krejci and Ryan Spooner, not to mention his locker room presence being significant. But at 32 and coming off his lowest offensive total in nine years, the bigger question is how does this move help bolster the Bruins’ blue line.

The short answer is it doesn’t. While Backes has put up good ironman numbers in career games played, his complementing offense and plus-minus might be enough to get Boston over the playoff hump. At 6-foot-3 and 220 pounds, he is a Mark Recchi type. Boston fans will like this guy.

But Backes is not likely to get Boston far beyond their current status of a fringe playoff team unless some help comes on defense.

After signing Torey Krug to a long-term deal, and John-Michael Liles to a one-year contract at a bargain $2 million, the Bruins are still in desperate need for another contributor on defense. The drafting of Boston University’s Charlie McAvoy at No. 14 overall is touted by most NHL insiders as a can’t-miss; but the current Terrier, who enters his sophomore season at BU this fall, is still a year or two away from making the short trip from Agganis Arena to TD Garden. Zach Trotman trotted off to LA, leaving the Bruins with Krug, Liles, Zdeno Chara, Adam McQuaid, Kevan Miller, Colin Miller and Joe Morrow as the current complement on defense.

Okay, raise that hand if you — and Tuukka Rask — think this group will get the franchise closer to a June parade on Causeway Street, let alone play in May.

The free-agent problem for Boston – and any other team needing help on defense –- is that that pool was shallow from the get-go. After Dallas paid $7.5 million per for 33-year-old Dan Hamhuis on Friday and Jason Demers opting to go to Florida after signing a 5-year, $22.5 million contract on July 2, the vault swung open for the Stars’ Kris Russell, and Pittsburgh’s Justin Schultz.

Yes, there is Luke Schenn, who was acquired by the Los Angeles Kings from the Philadelphia Flyers last winter. At 6-foot-2 and 229 pounds, Schenn brings monster size, dishes it out on opposing players and is a good shot blocker. But in the new NHL with its focus on speed and skill, Schenn will likely be at the end of the payday line — and not in Boston.

The aforementioned pair will get a big payday — in the 5-6 million range — based solely on supply and demand. Toronto is rumored to be the highest bidder for Russell, the former Flame traded for picks at the deadline. Russell at 29, and Schultz at 26, who came to Pittsburgh at the deadline from Edmonton, all have comparable offensive production (expect 30 points a season). Both can move the puck. Russell, however, has a better plus-minus and logs more power play time.

Russell is one of the top NHL shot-blockers, a major reason why the rebuilding Leafs want him to replace their aging former captain Dion Phaneuf, who went to Ottawa at the trade deadline.

It might be Schultz, however, who is the best buy for Boston. He is the younger of the two and comes off a pinch-me playoff season with the Penguins where he played in 15 games with four assists and won the Stanley Cup. At 6-2 and 193, he brings the most size of the three to a smaller Bruins D corps, Chara aside. While his plus-minus stats were an abysmal minus in “we-play-no-defense” Edmonton, he played at a plus-7 in 18 games in Pittsburgh.

Given a realistic choice, the Black and Gold should pursue Schultz. However, given the team’s reluctance to go long term, they may be priced for Schultz.

But, then again, they just opened Jeremy Jacobs’ wallet for six years for Backes. While hindsight is 20-20, don’t ruin your post-Independence Day plans with the reminder it’s only been a year since the Dougie Hamilton trade ($5.75 million).

Stay tuned – and keep scratching.