What would that be? That the only reason Ridley is getting such a big portion of the carries now is only cause of BJGE toe being banged up?
How does that explain is new duties on 3rd down then? Truth is, it doesn't. The coaches are starting to see what they have in Ridley, and he's getting better in pass protection, so he's getting more work.
He's getting more work because he's BETTER.
BGE is mostly a one-cut, straight-ahead power back. Given a decent push by the OC and OGs to open a hole in the middle of the LoS, BGE will nearly always get his 4 yards. First contact rarely brings him down, even when he's moving slow, unless its 3 guys jumping on his back simultaneously. Even then, he'll keep churning often for an extra yard or two. If a lone DB is trying to backfill the hole, BGE will usually run over him for another 5 yds, sometimes more. If the Pats have the ball with a 7-point lead with, say, 8:00 left in Q4, BGE is the guy I want pounding it up the gut against a tiring defense to help take 7:00 off the clock on a drive that puts the Pats up by two scores. BGE does NOT, however, appear to have the quicks necessary to hit a cutback when the middle closes and the play gets strung out toward the sideline.
Woodhead is nimble and fast with enough burst to slip through a tiny crack up the middle and get his 4 yds, sometimes more if the LB blinks. He also has the burst to hit the cutback that BGE doesn't. At the second level, he can often make the first guy miss for a couple extra yards. Though Woody runs tough and will break a mediocre tackle attempt, he's not likely to run through a squared up LB the way BGE can.
Both BGE and Woody, IMHO, appear to need a fairly solid blocking set, well-executed, to get going, especially up the gut. It's the kind of thing that often tips off a defense to what's coming. Both will usually get their 4 yards, and more, if a defender effs-up. But, if a Pats blocker gets beat or effs-up, they can be stuffed.
I believe that a major contributing factor to their lack of production up the middle this season is Koppen being out. I think that Koppen's run-blocking has been a bit under-rated or overlooked. His replacements have been pretty much fine on the snap and in passpro, but they don't seem to be able to make way for BGE and Woody (or even Ridley) up the middle with nearly the consistency that Koppen did last season.
Ridley, IMO, doesn't have quite the power that BGE does. He can certainly run through a tackle if he's "at speed", a couple steps after his cut, but he doesn't seem to have immediate power coming out of his cut that BGE often demonstrates (which may be partly a technique/footwork thing that he may be able to improve somewhat). Still, he's certainly more naturally powerful than Woody - he has the ability to power through LoS trash that might stymie Woody - and he doesn't go down as easily on first contact. However, he's not using that power with consistent effectiveness yet, which has led to him getting stuffed a few times (another likely development issue).
Ridley also (again, MHO) isn't quite as shifty as Woody (yet). He doesn't seem like he's able to run around a defender in the open field as "cleanly" as Woody often has. However, his natural power can compensate for that as he improves technique (timing on a lowered shoulder, stiff arm, etc.). But, he does appear to have some pretty good natural vision for the imminent hole, enough quicks to make the cutback on a strung-out play and a second cut to the outside when appropriate. I'm not sure that he has the top end to be able to outrun faster defenders and take it to the house from 80-yards out, unless the defenders who CAN catch him are seriously out of position, but from around mid-field . . .
Ridley's not quite at the point where his runs aren't being tipped off to the defense, but, with his combination of quicks and power, he has shown flashes of being able to do more than either BGE or Woody with a bit less than the optimal LoS blocking they need to be consistently successful. This, in combination with Koppen's absence, is probably why we've seen more of Ridley this season (perhaps earlier than originally planned). If he continues to develop at his recent pace, by this time next season, he could be making play-action and draws a lot more effective. This doesn't at all mean that there won't be a place for BGE and Woody. The Pats are always going to need those guys to make 1st-and-10 into 2nd-and five or to help chew clock in Q4 (when breaking a long run may not be quite as important). But this is still all based on
potential. He's not consistently "better" than BGE or Woody quite yet.
