There are two factors that determine the success of the run game. One is the running back. The other is run blocking. When the run game struggles, it is easy to say both at fault. I really do not think that is the case with the Jets, though.
Some say it is a 50/50 split in importance between the back and his blockers. I think a lot more goes on the blockers, though. A good back certainly needs to have the vision to identify holes, the speed to get through them, and the strength to grind out extra yardage once touched. When the line opens no holes, though, the back has no chance. Greene is getting hit in the backfield consistently. Even if he does not go down,he is slowed down or stopped and forced in a direction where another defender has an easy clean up tackle. Once one guy gets penetration into the backfield, a hole is usually opened for other defenders to follow.
There was one play last night where Greene probably did not read his blocks properly. He needed to cut inside instead of breaking to the outside trying to gain the edge. The rest of the time, he really had no chance. You are not going to gain yardage if you have no opening to get through.
Greene might not be a starting caliber back in this league, but what we have seen in 2011 offers no indication whether this is so. There is not a back in the league who could have success with the run blocking the Jets have provided him.