It was one of two penalties Dougie Hamilton was whistled for in a forgettable first period during a preseason game in Winnipeg last Thursday but it was also a telling moment.

The defenseman was called for an infraction after an opposing player he was battling hit the deck. For the 20-year-old that negative play had the faintest silver lining.

“Maybe with that one penalty maybe I wouldn’t have knocked that guy down last year” Hamilton said jokingly after the Bruins practiced Sunday at the Garden.

Entering his second NHL season Hamilton is still just a few months removed from being a teenager. He’s still growing and maturing and there’s a limit to how much stronger he can become year to year. Nonetheless fresh off skating in 42 games and posting 5-11-16 totals as a rookie he went off this summer to improve his strength skating and his ever-important defensive-zone play.

“I think it’s pretty much been stressed by everyone that I need to improve my defensive game” said Hamilton who noted that he’s watched tons of video with the coaches during camp. “I think if I’m playing against top-two lines then I really need to focus on that. . . . You have to be a lot more aware I guess and I guess more careful.”

Hamilton was a fixture in the Bruins’ first 39 games last season as he played top-four minutes (often alongside Dennis Seidenberg) and logged time on the power play. By the end of the season though Hamilton had already gotten a dose of how difficult it would be to keep his job as compared to winning it. Fatigue and some subpar play led to coach Claude Julien scratching the 2011 first-round pick (ninth overall) down the stretch and early in the playoffs. Hamilton skated in seven postseason games but Torey Krug’s emergence as a top-six option kept him from playing in the Stanley Cup finals.

In fact the development of Krug Matt Bartkowski and others created a competition for a couple of defense spots that Julien said wouldn’t be decided until tomorrow at the earliest. Two out of a group including Hamilton Krug Bartkowski and Kevan Miller will be scratched for the regular-season opener Thursday against Tampa Bay. It sounds like Hamilton has a strong chance of facing the Lightning.