​CHICAGO — Jeremy Garrett was in his office on Oct. 29, a Thursday morning, working on the game plan for an upcoming matchup with the Seattle Seahawks when he heard a knock on the door.Dennis Allen, his boss and the Chicago Bears defensive coordinator, stood in the doorway. Allen had some good news for his defensive line coach.But that’s underselling it. This was the type of seismic trade that happens only once a year across the NFL, if that. The Bears landed All-Pro defensive tackle Jeffery Simmons, sending two future first-round draft picks to the Tennessee Titans.Garrett’s first instinct was not to get too far ahead of himself.“Is it done?” he asked.His second instinct?Whew.His mind already was going through the mechanics of what Simmons’ addition would mean for the Bears defense. The deal would be finalized later that afternoon, and Garrett soon had Simmons sitting in his office asking how he could best prepare to face the Seahawks in four days.These were two Mississippi boys at heart. Garrett grew up in Senatobia, Miss., not far from the Tennessee border. Simmons grew up about a 2 1/2-hour drive southeast in Macon, not far outside Starkville. Garrett played at Ole Miss from 2004-07. Simmons, one of the top recruits in the country in 2016, stayed home to play for Mississippi State from 2016-18 before jumping to the NFL.Garrett followed Simmons’ career from afar, from when Simmons was the top recruit in the state to becoming a first-round draft pick to emerging as one of the NFL’s best defensive tackles with the Titans.To see him now — across the desk in his office — was a defensive line coach’s dream.“I always knew about him as a player and a person and what he’s done in the community,” Garrett said. “But that was the first time we got together.”They were in the office past 10 p.m. that first night. Simmons played 86.6% of defensive snaps through the first seven games of the season with the Titans. He’s one of the few defensive linemen in the NFL who rarely comes off the field. Not even Myles Garrett had that heavy of a workload last season when he set the single-season sack record and won his second NFL defensive player of the year award with the Cleveland Browns.The Bears intend to give Simmons a similar heavy workload. But if he was going to do that in his first game, just four days after the trade, he was going to need a crash course in Allen’s defensive scheme.“And you could just tell (he was like), ‘I want to make sure I’m not going to cost the team,’” Jeremy Garrett said. “ ‘I want to do everything, I want to be aligned correctly, I don’t want any mental errors.’ You could just tell the passion he has about doing his job and doing his part.”Simmons played 87.3% of defensive snaps in his Bears debut Monday in a 34-17 win against the Seahawks. He recorded a sack, one pass defended, two tackles for a loss and a team-leading six tackles. He was a force for a Bears defense that, in some