Green (6 feet, 195 pounds) is taller but slighter and probably has better range.
"We watched tape last year on Mike Green, and Mike's big plays were when he was playing (off the line in coverage)," defensive coordinator Ron Rivera said. "We also saw that Mike Brown is an aggressive football player, a tremendous blitzer based on stuff we saw from the '03 defense and before he got hurt (in 04), and that he's a box safety."
Brown played in just two games last season before suffering a ruptured Achilles tendon. While he intends to be back in the best shape of his life and there are no indications he won't be 100 percent at the start of training camp, even if Brown is a half-step slow initially this summer, strong safety would suit him best.
"In college, I was a safety that was up towards the line of scrimmage a lot," said Brown, who led Nebraska in tackles three seasons in a row. "I feel real comfortable in the box. I like to play physical football and usually at that position you get a chance to play some physical football. I'm going to enjoy it. That's my favorite part of the game and hopefully I'll do pretty well at it this year."
The 5-foot-10, 212-pound Brown isn't the prototypical linebacker-sized strong safety, but he's big enough for Bears coaches.
"He's not tall, but there have been a lot of good ones who were short because they're stout, and they're football players," Rivera said, "and that's what he is."
Rivera denies that Brown's injury, the first of his NFL career, had anything to do with the switch to strong safety.
"The biggest thing is how stout he is," Rivera said. "When you look at the two of them and stand them side by side, you say to yourself, 'This is the guy that's probably best suited to be a strong safety,' and that's a big part of the reason we're doing it."
As a 16-game starter at strong safety in 2002 and '04, Green was second on the Bears both seasons with 138 and 132 tackles, respectively. The sixth-year veteran had two interceptions last season but only one in the previous four seasons.
"I'm happy with the move," Green said. "I'll be back there roaming the field and just trying to make plays. It will help me use my range a little bit more. Now I can run and play the deep ball and run from sideline to sideline. At free safety I can freelance and read everything."
Brown has developed a reputation as a big-play guy. He had a 95-yard fumble return for a TD in the second game last season before his injury. Also a sixth-year veteran, he averaged 99 tackles in his first four seasons with 11 interceptions, three of which he returned for touchdowns, including back-to-back overtime game-winners in 2001.