The 49ers hired Jim O'Neil to be their defensive coordinator.
CSNBayArea.com's Matt Maiocco broke the news on Tuesday.
On Wednesday morning, Greg Cosell -- Senior Producer of NFL Films -- explained what San Francisco is getting in the 37-year old coach.
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"I can go very deep in the name of full disclosure. Jimmy is a good friend of mine. I know his philosophy and I know a lot about him," Cosell told KNBR 680. "There's a big belief in pressure, and differnet kinds of pressures. He's been mostly a 3-4 guy, but there's a lot of hybrid concepts with 4-3 principles as well.
"There's a lot of dimensions to what Jim wants to do, now much of that depends on personnel, and obviously he needs now to evaluate the 49ers' personnel, and that will dictate I'm sure how much pressure, how much coverage, but he's very multiple just by his thought process and he likes to be aggressive."
In 2013, O'Neil was Buffalo's linebackers coach. The Bills were second in the league with 57 sacks.
[REWIND: Kelly's vision for 49ers: 'I want them to be fearless']
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In 2014, O'Neil's first season as Cleveland's defensive coordinator, the Browns were ninth in points allowed (21.1) and 23rd in yards allowed (366.1).
In 2015, the Browns were 29th in points allowed (27.0) and 27th in yards allowed (379.2).
"Obviously, people are gonna look at Cleveland's defense, which was not very good this year," Cosell said. "And it was not very good for a number of reasons. But I think he's a bright young coach. Now, don't forget, when you're young as a coach, you go through a learning process as well. That's part of the gig. People just automatically assume that because these guys are coordinators they know everything.
"You go through a learning curve in anything you do when you're fairly new at it, and I think Jim probably went through that in Cleveland. They had some struggles on the defensive side of the ball ... I would expect him to have learned and be better."
It won't be easy, though.
With Chip Kelly running an up-tempo offense, his teams during three seasons as head coach of the Philadelphia also had to defend more plays than any other team in the NFL. The Eagles faced a league-high 1,148 plays last season, second-most at 1,113 in 2014, and the most in 2013 with 1,150 defensive plays.
"If you're gonna be the defensive coordinator for Chip Kelly, you're going to rank low," Cosell declared. "Fans need to understand that because they play a lot of plays. It's hard to be ranked 10th or 11th because it's just hard. That offense impacts the whole team. It's not just an offense."
As Cosell made very clear, he has a relationship with O'Neil and wants to see him succeed.
"I'm friends with him, I think he's really sharp," Cosell said. "I think he's really passionate. I think he really cares. I think he's a bright young coach ... Now it comes down to, 'What's the talent?' Can you be significantly better without a significant influx of talent?
"And as I said, no matter how much better the talent might be, the numbers will probably not be great because you're the defensive coordinator on a Chip Kelly team."