Dannell Ellerbe (59), Bryan Hall and the rest of the Ravens’ D are hitting their stride. (US Presswire)

After struggling on defense most of the season, the Ravens are one of the NFL's top units the past six games. In that span, the Baltimore has allowed 299 yards per game, which ranks fourth-best. In Baltimore's first 10 games, its defense gave up 382.3 yards.

The Ravens are giving up an average of 23 points over the past six games, although that includes defensive touchdowns by the Broncos and Bengals. Take those scores away and the Ravens are giving up 20.6 points per game, which is just under the season average of 21.5.

"We are playing fundamentally better," Ravens coach John Harbaugh said. "We are on the same page better. Our coaches have done a great job continuing to coach -- every single week, every little thing. You can improve throughout the course of the season. Our team has done that every year."

Making this situation unique is that Baltimore's defense has three players that began the season on the practice squad -- LB Josh Bynes, LB Adrian Hamilton and S Omar Brown. Injuries to LB Ray Lewis (triceps), LB Jameel McClain (spinal cord contusion) and S Bernard Pollard (chest) forced the trio into the rotation in recent weeks.

Against Cincinnati, in a game where both teams rested the majority of their starters, Bynes led the Ravens with nine combined tackles.

"We wouldn't be where we are at with the circumstances that we faced if our young guys hadn't played really well and played winning football," Harbaugh said.

Defending Luck: Colts QB Andrew Luck hasn't played like a rookie this season. In 16 regular season games, Luck threw for 4,374 yards and 23 touchdowns, although he had 18 interceptions.

Luck helped lead the Colts to five wins in their last six games, including a 28-16 victory over AFC South champion Houston last Sunday.

"He's a great quarterback," Ravens DT Haloti Ngata said. "If you watch the film, he does a lot of great things. He's mobile, he's faster than you think he is. He's bigger than you think. He does a lot of good things. I hope we can just make him look like a rookie out there instead of a veteran quarterback."

Injury report: DT Ngata (knee), RB Anthony Allen (head), TE Billy Bajema (head), WR Tandon Doss (ankle), CB Chris Johnson (thigh), FB Vonta Leach (knee/ankle), DE Pernell McPhee (thigh), RB Bernard Pierce (ankle), S Pollard (chest), LG Jah Reid (toe) and RG Marshal Yanda (shoulder/knee) were limited in practice Wednesday.

Full participants: WR Anquan Boldin (shoulder), LB Dannell Ellerbe (ankle), DE Arthur Jones (thigh), LB Lewis (triceps), LB Albert McClellan (shoulder/thigh), RT Kelechi Osemele (knee), S Ed Reed (shoulder), CB Jimmy Smith (sports hernia), WR Torrey Smith (knee) and OLB Terrell Suggs (biceps).

Follow Ravens reporter Jason Butt on Twitter: @CBSRavens and @JasonButtCBS.