I think they are protecting the hand he had surgery on and his body in general.
http://www.rotoworld.com/recent/nfl/6557/robert-quinn
Rams OLB Robert Quinn said he's recovered from the hand surgery that sidelined him during OTAs.
Quinn admitted his hand was "messed up a little bit," but expects to be ready for the Rams' first practice on Saturday. The former first-team All-Pro is hoping for a bounce-back year after recording a career-worst four sacks last season. Jul 28 - 4:52 PM
Source: Joe Curley on Twitter
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I think you're down on Quinn Boni because of the past injuries. Quinn is a difference maker when healthy. He is made for this defense and they need him playing. The Rams haven't gotten great pressure thus far in preseason. The Rams will be smart with Quinn but, they will start him. If had to guess I would say 75% of defensive snaps. He has to be out there in the first quarter, end of the half and the fourth quarter. I haven't heard of any setbacks so I assume he could play now if it were the regular season. We will have to keep up on his status.