Harbaugh saw how offenses were putting up pinball-type numbers with their passing games, and he figured it was inevitable that opponents would be able to move the ball up and down the field. So instead of sweating over escalating yard totals, he placed extra emphasis on the most important chunk of the field: the final 20 yards.
"I'm not sure why people are so enamored with yards," the coach said. "Yards are important and they're valuable, but they keep track of the points on the scoreboard. And you control the points in the red zone mostly. So we felt like if we could be great in the red zone, we'd have a chance to control points. So we practice it every day. It's something that's an emphasis for us."
It has paid off. While the Ravens are 4-6 heading into Sunday's home game against the New York Jets, red-zone defense has been among their strengths. No defense has been better this season when it comes to keeping opponents from scoring touchdowns once they cross the 20-yard line, especially at M&T Bank Stadium, where they have allowed just one, a league-best.
The Ravens are 13th in yards allowed this season, but have the eighth-best scoring defense.
Players and coaches chalk up their success to a combination of scheme, swagger and less space for offenses to operate. But another significant factor is how much time the coaching staff spends studying the tendencies of opponents and disguising their own.
While the Ravens were no slouches in the red zone in Harbaugh's first three years, finishing in the top five in red-zone defense in each of those seasons, no defense has been better since 2011. The Ravens, who ranked first in 2011 and second in 2012, have allowed touchdowns on just 37.2 percent of opponents' red-zone trips since the start of the 2011 season, tops in the NFL.
"It starts with Coach Harbs emphasizing red zone from the get-go," weak-side linebacker Josh Bynes said.
The Ravens compete in red-zone drills nearly every practice, and those are some of the only times that the first-team offense and first-team defense duke it out during the week. Every Friday, the staff conducts a red-zone defense meeting, which Harbaugh sits in on. And the short-yardage and goal-line drills later that day are among the week's most spirited.
This season, the Ravens have allowed nine red-zone touchdowns in 28 trips and that 32.1 touchdown percentage is the NFL's best since the 2001 Philadelphia Eagles (30.4 percent).
"Just attitude," middle linebacker Daryl Smith said when asked why the Ravens defense has been so dominant in the red zone. "That's our end zone, and we don't want anybody in it."
As offenses approach the end zone and the threat of the deep ball disappears, the defensive backfield becomes more congested, passing lanes narrow and angles for the running backs become more acute.
Plays must develop faster near the goal line because cornerbacks press closer to the line of scrimmage and linebackers and safeties stack the box, making running difficult. The Ravens have allowed just one rushing touchdown in 2013.
Offenses have go-to plays in the red zone. The Ravens identify them in film study and prepare for them in practice while also trying to keep the offenses guessing.
"There are times to take risks, and there are times where we have played not very high risk, played coverage and played well," defensive coordinator Dean Pees said. "I think the key thing is … don't do the same thing all the time."
They changed up their looks against the Chicago Bears in last week's 23-20 overtime loss.
In Chicago's first red-zone series, when the Bears had six cracks at the end zone from inside the 10-yard line and couldn't score, the Ravens at first blitzed heavily while playing tight man-to-man coverage on the outside. But on the final third-down stop, they instead dropped seven defenders into coverage and cornerback Jimmy Smith batted down a pass.
In the next two red-zone series, the Ravens tried to confuse Bears quarterback Josh McCown with creative coverages. On one play, strong safety James Ihedigbo blitzed while rush linebacker Terrell Suggs dropped into the end zone. On another, the Ravens showed a heavy inside blitz, backed out of it, put seven defenders in coverage and got a sack.
"He's very creative," Harbaugh said of Pees, who joined the staff in 2010. "Dean brought in a lot of ideas. We've really evolved our red-zone package since Dean has been here and he spearheaded that. We're pretty multiple down there. It's hard to predict what we're going to be in and how we're going to play things. It seems like it is giving people a lot of trouble."
On Chicago's only red-zone touchdown, which came on a screen pass to running back Matt Forte, Baltimore had a sound scheme but five defenders couldn't make the tackle.
That rare breakdown did not sit well with the Ravens, who want the red zone to be a dead zone.
"We talk a lot of pride in it," defensive tackle Arthur Jones said. "It's like someone being in your backyard. We just fight and keep guys out of the [end zone]. We work hard at it, coaches included. We go over it so much in practice. It's something we really emphasize. Keep them out of the end zone and good things happen."