Pushing, grappling, colliding, chopping and punching for a few seconds every snap, the undersized Gregg plays a critical role in the Ravens' transition to the 3-4 defensive alignment.
"Kelly Gregg is tough," Ravens Pro Bowl outside linebacker Peter Boulware said. "You tell him his job and he puts his hard hat on, gives it everything he has and does that for you every day."
Gregg has the perfect background for a position that demands quickness, brute strength and a stout build. He was one of the top heavyweight wrestlers in the nation as a prep senior at Edmond High School (Okla.), winning a national junior heavyweight title.
"Playing nose guard is very similar to what I did in wrestling," said Gregg, on his third NFL team at age 25. "It's all about leverage and balance. The lowest man wins. You get under people's pads. You can never underestimate anybody.
"Being a wrestler is just like being in the trenches."
During Friday night's preseason game against the Philadelphia Eagles, Gregg took another opportunity to prove his doubters incorrect.
The Eagles claimed Gregg off of the Bengals' practice squad in 1999, but cut him after training camp when the lineman didn't want to accept a demotion to the practice squad from the active roster.
Prompted by defensive line coach Rex Ryan's recommendation, Baltimore signed Gregg the day after Philadelphia released him. Ryan was Gregg's defensive coordinator at the University of Oklahoma in 1998.
With the Ravens last season, Gregg played in eight games with one start to finish with 19 tackles, 10 solos, a sack and one tackle for a loss.
"I just thought Baltimore was a better place for me, because I didn't want to be on a practice squad," said Gregg, who was drafted in the sixth round by Cincinnati in 1999. "I've got no bitterness against the Eagles. It's the business world. You move on.
"It worked out good for me in Baltimore, though you never know. You can never relax."
While the Ravens lost a war of attrition against age and the salary cap to lose tackles Sam Adams, Tony Siragusa, Lional Dalton and Larry Webster, Gregg became a target this off-season.
Among the inadequacies that critics cited against Gregg becoming a starter:
His stubby arms.
Being too short with a generous listing of 6-foot-tall on the Ravens' roster.
Not being bulky enough at 285 pounds, although Gregg is actually a few biscuits over 300 pounds now.
"I'll never pass the scouts' eye test," said Gregg, referring to his lack of physical stature. "Most people in the NFL see guys and say, ‘He's too small.'
"It took an organization that was willing to take a long, hard look at me to find a home. Rex knew me and knew what I could do."
As a senior at Oklahoma, Gregg recorded 117 tackles, setting a Sooners' record with 24 tackles for losses. He also turned in nine sacks.
Competing in NFL Europe when Baltimore allocated him to the Rhein Fire before last season, Gregg led his team with six sacks and three forced fumbles along with 40 tackles and three pass deflections.
Because of injuries to Michael McCrary and Anthony Weaver, Gregg has been forced to start at defensive end this preseason even though he's far from ideal height for that spot.
"Kelly's one of the most solid defensive linemen," Boulware said. "He brings it."
Ravens coach Brian Billick has made it plainly obvious how highly he thinks of Gregg, particularly his attitude. Billick said Gregg has never shirked any assigned duties, even volunteering to pitch in at practice as a tight end, offensive guard, fullback and linebacker.
"The guy just loves to play football and will do whatever you want him to do and now has found a spot as a starter," Billick said. "Great story."
Even though Gregg hasn't established himself in extended regular-season action, he has become something of a fan favorite. He resembles some of them. He's proud to call himself a blue-collar guy.
Siragusa dubbed him "Buddy Lee" after a stocky figurine featured in a national jeans commercial. The moniker has stuck.
"I'm just like the fans, not real big, and not everyone has great size," Gregg said. "I'm just like the people in the city of Baltimore. They're hard workers, and that's what I am.
"This is the best job in the world. I love football and I don't take anything for granted. I'm not going to change the way I approach my job."