Roberson completely tanked the pre-draft process. He did not interview well nor have good workouts at the 2014 NFL Combine or at his pro day. Questions regarding his work ethic surfaced and combined with his durability issues to drop him out of the draft.
Fast forward a year, and Roberson has significantly changed his fortunes. His is in good standing with Rams Head Coach Jeff Fisher and was held in high enough regard to earn two starts (KC, @SEA). While he largely held his own, it's worth noting that it was against sub-par WRs.
The CB group is very talented overall - but they still have a lot to prove. There are two fairly well defined 2 groups: those that have established themselves and the unproven players. The former include Janoris Jenkins, Trumaine Johnson, and E.J. Gaines. The latter includes Lamarcus Joyner, Montell Garner (preview), Imoan Claiborne (preview), and to an extent Brandon McGee and Roberson.
Gaines, Johnson, and Jenkins are all but locks to make the roster. Given that he started last year, it'd be easy to pencil Roberson into that 4th spot, but there is a lot of competition to be had between him, Joyner, and McGee to determine the pecking order at CB. Given Joyner's potential to move around the secondary, I'd argue that Joyner should get the nod. Which leaves Roberson fighting with McGee for the final CB roster spot.
Improvement. Roberson has talent, but will have to show improvement to stay ahead of McGee on the depth chart. If competition breeds progress for the Rams DBs in camp, this competition could enable the defense to finally take that next step as a unit.
Chances of Making Roster (7/10)
Barring another lackluster offseason, Roberson will be on the roster. Given his 2 starts last season - and that the 2nd start came in a game that Jenkins and Johnson also played in - I think it's safe to say that he'll beat out McGee and return to the 2015 squad.