Clark is coming off an up-and-down 2013 season. The Steelers declined to make Clark an offer before he hit free agency after having been with the Steelers since 2006.
He's made a name for himself among NFL media types, having appeared several times in the past two years on various ESPN talk shows. It would seem he'd be able to make a good chunk of money (well into the six-figure range) talking about football as opposed to playing it. He'd deal with significantly less risk too - assuming he's not in the immediate path of a stumbling Warren Sapp.
The Steelers drafted Shamarko Thomas in the fourth round of the 2012 draft, and signed Mike Mitchell to a five-year deal this March. Thomas is expected to eventually replace Troy Polamalu as the team's strong safety, and Mitchell will replace Clark as the team's free safety this year.