Kelly spent the previous 10 years with Tampa Bay, and he knew many Lions who used to be Buccaneers, including coach Rod Marinelli, defensive coordinator Joe Barry, secondary coach Jimmy Lake and several players. He knew the Tampa-2 system, and he came to Detroit along with cornerback Leigh Bodden and safeties Dwight Smith and Kalvin Pearson.
But entering this Sunday's game at Minnesota, the Lions are 0-4, rank last in the NFL in total defense and are the only team without an interception.
And Kelly dressed but didn't play a down in the Lions' last game, a 34-7 loss to Chicago.
"Obviously I was unhappy with it," Kelly said. "I mean, you know, I'm suited up. I'm not suited up. I'm suited up. I'm suited up to play. If I'm standing there with my T-shirt on and sweats and a Lions cap, I know I'm not playing. But I was suited up to play, and it didn't work out that way."
Did Kelly voice his feelings to the coaches?
"No, because I don't need to," Kelly said. "They know I'm not happy with it. But that was the decision that they made, and as a player, I just have to deal with it."
Defensive coordinator Joe Barry said the Lions did not enter the game with the intention of not playing Kelly. They wanted to give Keith Smith some playing time, and in the course of the game, they just didn't put in Kelly.
"He was upset and he was frustrated," Barry said. "Like I said, we told him just like I'm telling you guys. That was not the plan to not play him. It happened that way. Brian's going to be up and running and play this week."
Told what Barry said, Kelly smiled.
"My perspective is, it's a coach and a coaching staff looking for answers," Kelly said. "I can't put myself in the game. They obviously made a conscious decision to go in the direction they went in. I've just got to be the character guy that I am and deal with it."
But Kelly added: "I don't think what he said is a lie. Don't mistake it for that."
What's the plan going forward? Travis Fisher has a knee injury, and Barry said Smith was in the mix to play, but not to start.
"I honestly don't know," Kelly said. "I'm just going to go out there and continue to do what I do and work hard. I can't control those issues. Those are coaches' decisions, and I don't think right now - from the top to the bottom - nobody knows. I just think it's one of those things, we're trying to get a win and get a rhythm and some better play out there on the field."