As VA Official points out, you definitely need to read 2-3-4c and 2-3-5b together with 9-2-1c and 9-2-3c to get the full picture. The first two say that you can pull an opponent to get to a loose ball (or to the runner, if you're a defender), the latter two say that you may not grasp or hold "in an effort to restrain an opponent", with no exceptions provided.
The way I've always interpreted this is that you can move opponents out of the way, including by grabbing them, to make your own path to a loose ball or the runner, but not to make a path for a teammate nor to simply keep them out of the play.
Hence, the pull-and-shoot (DL pulls OL down/aside so that LB can charge through the hole) is illegal, but if the same DL grabs the OL and tosses him aside so that he can get to the QB, that's OK. (If the OL does this, though, it's a foul - he's not trying to get to the runner or a loose ball.) Similarly, if you grab and pull and opponent out of the way as you dive for a loose ball, no problem. Grab him so that your buddy can dive on the loose ball, foul.