49ers free-agent report: Perrish Cox

The San Francisco 49ers have 14 potential unrestricted free agents who would hit the market when the new league year begins on Tuesday. Let’s continue our countdown with a cornerback who surprised many with a breakthrough season last year.

CB Perrish Cox

Originally a fifth-round pick of the Denver Broncos in 2010 out of Oklahoma State, Cox has also played for the Seattle Seahawks and has had two tours of duty with the 49ers.

49ers career: He was merely supposed to be the Niners’ nickel defensive back last season but was forced into action when starting cornerback Tramaine Brock suffered a toe injury in the opener at Dallas. Cox started a career high 14 games last year and his career-high five interceptions -- he had one in his career entering 2014 -- led the Niners.

Argument for keeping Cox: He stepped up early and became a fixture, as evidenced by his plus-6.7 coverage grade and 42.3 passer rating against in the first half of the season, per Pro Football Focus. So why not build on it and his newfound maturity? It’s paydirt for the 49ers.

Argument for letting Cox walk: He faded in the second half of the season, a minus-7.3 coverage grade and a 109.6 passer rating against, per PFF, so offenses figured him out as he wore down and a big payday would be a mistake. It’s fool’s gold for the 49ers.

A bold prediction: Cox, 28, may not command the type of money that younger fellow UFA CB Chris Culliver will, and that’s OK with Cox, who is a fan of new coach Jim Tomsula and wants to return to Santa Clara and build on last year’s success. I think he returns.