Fuller was drafted in the sixth round in 2013 and made the practice squad last season, but Caldwell said that the player is now really starting to get to grips with the club's plays.
"It's big because of the fact that they get some extra reps in," Caldwell told the club's official website. "He was on the practice squad, obviously, a year ago and did have an opportunity to come in and still work and try to improve his craft.
"Because the system is new, it kind of gives him a little bit of a head start in that regard. He was able to grind through it on the weekend and did a nice job. He was also able to kind of pave the way for some of the guys that had not.
"He's been doing it for five weeks now, I guess, so he's a good bell cow for us. He set the stage for us in that regard, but he was absolutely outstanding."
The wide receiver was the 171st overall pick last season.