Here is an Approved Ruling from last year's rules that show if you are eligible to touch OR recover a ball, you can push someone in the back on the way to it.
A.R. 6.57 KICKOFF—BLOCK IN BACK BY TEAM A
On a kickoff or safety kick, A2 and B3 are running downfield together. The ball hits the ground in front of return man
B7 at the B10, where he picks it up and runs it to the 50. A2 pushes B3 in the back (a) at the B40 while the kick is in
the air; (b) at the B17 as he scrambles for the ball after it has hit the ground; or (c) at the B20 while B7 is running
with the ball.
Rulings:
(a) B’s ball, first-and-10 on A40 or re-kick after 10-yard penalty. Team A may not block in the back while the ball is
in the air during a free kick.
(b) B’s ball, first-and-10 on 50. There is no foul for a block in the back when a player is making a personal attempt
to recover a loose ball he is eligible to touch or recover.
(c) B’s ball, first-and-10 on 50. There is no foul for the kicking team blocking in the back during the return, as they
are now the defense.