LAKE FOREST, Ill. -- At the newly renovated Halas Hall, which now teems with security, coach Marc Trestman often invites visitors to speak to his players about what they should already know.

Mike Singletary told them. Mike Ditka did, too. Otis Wilson and Gale Sayers also spoke to Trestman’s club about what it means to be a Chicago Bear.

“The one thing we’ve done this year, we’ve tried to bring, tried to do a little bit more -- because we’ve got so many new faces -- [is to bring in former players to explain] what being a Bear is all about, you know?” Trestman said. “Being a Bear starts on the defensive side of the ball, and with the mentality of what a Bears defense plays like. We just want to reinforce that. We’ve got a lot of new guys and understanding what it is to play for the Bears means play[ing] tough defense.”

For a variety reasons during Trestman’s first year with the club, the Bears drifted away from that. During former coach Lovie Smith’s tenure (2004-2012), the Bears ranked in the top three in 10 -- yes, 10 -- statistical categories. First in takeaways (310), second in interceptions (181), first in fumble recoveries (129), three-and-outs forced (485), third-down conversion percentage (34.1) and opponent red zone scoring efficiency (79.3 percent).

It all vanished when the organization ushered Smith out the door and hired Trestman.

In Trestman’s first season, the Bears allowed the most points (478) in franchise history, the most total yards (6,313) and rushing yards. But injuries did cost the defense a total of 55 games last season, and that’s not taking into account losing defensive lineman Turk McBride to a ruptured Achilles and Sedrick Ellis, who retired on the eve of training camp.

No Bears opponent scored less than 20 points last season. But injuries, inexperienced backups and ineffective coaching at some positions played a role, as did other factors such as limited practice repetitions for the defense. According to multiple sources, Chicago’s defensive players over the course of a week of preparation for an opponent typically received approximately half the practice repetitions they had normally taken under Smith’s staff as offensive preparation had become a premium with the new regime.

After last year’s 8-8 season, general manager Phil Emery, Trestman and defensive coordinator Mel Tucker huddled to look at possible solutions. By March at the NFL combine, Trestman and Emery -- in discussing the team’s plans for free agency and the draft -- were already starting to use the word “tough” to describe the types of players they wanted to add on defense. In fact, for some in the organization, toughness trumped star power.

“We weren’t the tough team we wanted to be for a lot of different reasons,” Trestman said. “We want to accentuate it this year.”

To do that, the Bears brought in reputed tough guys such as Jared Allen and Lamarr Houston to add to the defensive line, in addition to re-signing Jeremiah Ratliff. They fired three defensive coaches and brought in another trio with reputations for being hard-nosed personalities with the ability to teach.

“We’re a team that wants to play -- even offensively -- with a defensive mentality,” Trestman said. “There’s a way to play football in Chicago, and that’s to be tough and physical, set a vertical edge, violent shed and run to the football. We’ve got to practice that way every day to be that team we want to be. We’re not there yet. We know that. We’re trying to get there because that’s the way every team plays in the National Football League. The best defenses play tough and physical. There’s a lot of different ways to win, but you seldom win a game [in which] you don’t win the line of scrimmage. There’s seldom a game you win where you can’t at least somewhat run the ball effectively and stop the run.”

Trestman pointed out that the whole “toughness” storyline can be overblown, correctly stating that the attribute is a prerequisite for any player or team in the NFL. “So to start writing stories, I think is just over-exaggerating,” Trestman said.

It is. But breaking down the importance of knowing what it takes to play Chicago’s brand of football is not. Of Chicago’s league-high 27 Hall of Famers, nine of them played defense. Since the first Bears players started earning Pro Bowl recognition in 1951, 119 of the club’s 226 selections have been defenders.

The Monsters of the Midway nickname came about due to dominant teams from the ’40s, which featured rough and tumble defenses. In Chicago, its defenses have always maintained a certain identity.

So while it’s certainly refreshing to see Chicago’s offense finally blossom under Trestman, the coach is correct in his attempt to make sure the club doesn’t stray from its roots.

“We need to be tough in our front, in our front seven and throughout our football team, throughout our defense,” Tucker said. “We preach that every day and they seem to want to be like that.”

Whether they will be, we’ll soon know.