ENGLEWOOD, Colo. — Replacing is a two-man job: filling in at every-down weakside linebacker and finding an understudy at the second nickel linebacker spot for the man who moves from the sub package to playing all snaps.

The first half of that contingency plan is obvious to anyone who watched the Broncos’ first three regular-season games this year: Brandon Marshall. Pegged as a nickel linebacker during training-camp work, Marshall stepped into the every-down role after Trevathan’s injury on Aug. 12 and adjusted to the workload over the following six weeks.

When Trevathan succumbed again to a fracture just above his knee on the second play of Sunday’s game, Marshall knew the drill: he changed helmets to the one equipped with a radio receiver to hear Defensive Coordinator Jack Del Rio’s calls, and went to work.

“Our defense, we never flinch,” said Marshall. “So I just came in and I’m like, ‘Let’s go, man.’ We live for this.”

Added defensive tackle Terrance Knighton: “B-Marsh stepped up to the plate, he came into the huddle and told the defense, ‘We’re going to win this game,’ and that’s what you want to see from a guy you wouldn’t expect that from.”

But the big change came when the Broncos used their nickel alignment. In Weeks 1-3, starting middle linebacker Nate Irving worked in the nickel sub package. Sunday, that role belonged to rookie Corey Nelson, who led the Broncos with seven total tackles: three solo stops and four assists.

Like Chris Harris Jr. in 2011 and Trevathan in 2012, among others, Nelson, a seventh-round pick, earned his promotion on the practice field and in the meeting rooms.

“He’s a …read more