I am excited about the potential for this signing and cautiously optimistic that it will pay off in a HUGE way. Like Marshawn, Lacy is a bruiser with innate tackle-breaking abilities who struggled with consistency during his first four years in the league. He doesn't have Marshawn's elite vision or leg-driving power, but if healthy, properly conditioned, and motivated, Lacy has at least a chance to serve as Marshawn-lite.
The offensive line is also hypothetically set up fairly well to support a bruising RB like Lacy. Britt, Glowinski, and Ifedi showed flashes last season of becoming explosive run blockers. Luke Joeckel is another physical run blocker and a definite upgrade in that regard over Gilliam.
This doesn't mean we are giving up on Rawls and Prosise either. Prosise, in particular, should become the dynamic complement to Lacy.Rawls on 3rd downs; the lightning to Lacy/Rawls' thunder. Rawls also has terrific potential, but he is still too unproven to rely on him alone as our workhorse back.
Basically, this signing just increased the likelihood that the Seahawks will return to being one of the league's premier rushing teams in 2017, when you factor in Carroll's offensive philosophy and track record, the expected improvement of the run blocking, and a healthy Russell Wilson.
Lacy is also a pretty good pass protector, which is an aspect of the position that Rawls and Prosise tend to struggle with. Carroll said Lacy's rehab from his October ankle injury is currently making it hard for him to condition, but that he should be back to around 240 lbs by the season.
The prospective for him to thrive in Carroll's balanced offensive attack should be tantalizing enough to motivate Lacy to get in shape once his ankle has healed. This signing took balls and vision. I'm glad they managed to get it done.