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B/S - The biggest improvement will be seen in the Safety room on D and WR room on O (based on overall group improvement in route running and body technique).
(Buy) Yeah, I'll go with that, although I think the defensive line room deserves a shout out as a possibility.
I don't know why it would be expected more so with the wide receivers than the others. Watch the bowl game and they still couldn't get separation from the DB's with Coleman coaching them (granted only one game). They still just run a very plain route with no moves to get the the DB's off balance. Very easy to read and cover routes when there are never any double moves or the receivers do not try to get the DB's off balance.
Perfect example is the Ravens/Titans game this weekend. Route run up the middle on one of the better DB's and the receiver plants his foot in the turf and takes a step like he's going on a flag route and then plants again and turns it up to the post and had the DB spun around wondering where he was. Easy long touchdown. Why can't we get someone to teach or receivers how to run routes and get the DB's off balance and get wide open?