Colin Kaepernick is a free agent. The particulars of why that remains the case are up for debate and the spectrum of reasons run from "He's obviously being blackballed by the league," to "He's just not very good." But that could be changing. Ravens coach John Harbaugh told reporters Thursday that "he wouldn't rule out" signing Kaepernick now that Joe Flacco is sidelined with a back issue, reports CBS Sports NFL Insider Jason La Canfora.

Harbaugh told reporters that he has been in contact with Kaepernick for much of the summer and the interest from the organization is definitely there. Ultimately, it will be up to the quarterback to decide what he wants.

Kaepernick played his best football under Harbaugh's brother, Jim, in San Francisco. But Jim Harbaugh left for Michigan after the 2014 season, and Kaepernick has struggled to recapture the form that helped lead the 49ers to the Super Bowl in 2013.

In April, after Kaepernick hit free agency, first-year 49ers coach Kyle Shanahan explained why Kaepernick's style -- which isn't that of the prototypical drop-back passer -- could be problematic.

"Usually a really good football player is a good football player in every scheme," Shanahan said. "I think you can get a little more into specifics when it comes to maybe the quarterback. ...

"€If you bring in a quarterback who is the best when he's a dual threat and can do all those type of things, that affects an entire offense. That doesn't just affect one guy. That's a huge commitment to your entire team. So, when you bring in someone like that when you're going to have to tinker the offense to fit one player, you've got to know you're tinkering every single person on that offense, too. So, when it comes to the quarterback and some O-linemen, you look into that a little bit more. After that, I think it's all pretty overrated."

In May, Giants co-owner John Mara said that some fans threatened to boycott if the team signed Kaepernick.

"All my years being in the league, I never received more emotional mail from people than I did about that issue," Mara told's Jenny Vrentas. "If any of your players ever do that, we are never coming to another Giants game. It wasn't one or two letters. It was a lot. It's an emotional, emotional issue for a lot of people, more so than any other issue I've run into."

And, in a new poll from JD Power, respondents said the national anthem protests sparked by Kaepernick were the main reason they tuned out NFL games last fall. 

And earlier this month, former NFL quarterback Michael Vick told FS1 that Kaepernick's predicament "has nothing to do with him being blackballed [for his social justice protests]. The gesture that he made last year when he took the stand to do what he did -- listen, we all appreciated it, we respected it and it was a good thing. I really think the stand that he took has nothing to do with him not having a job of playing in the National Football League right now." Instead, Vick reasoned, Kaepernick's employment situation was a function of his poor play on the field.

Apparently, John Harbaugh isn't concerned about Kaepernick, the NFL quarterback or social activist. As it stands, with Flacco out for at least a week, the Ravens have Ryan Mallett and Dustin Vaughan behind him on the depth chart. The team has its first full practice on Thursday.