Free Throw Lane Restrictions

[jer166]

We had our first unit meeting last night. While receiving instruction on the Free Throws Rough Play POE the discussion centered on the statement, "Coaches must not teach players to "lock up" arms along the lane line…

One of the instructors said to tell the players they can only hold their hands straight up or down. I asked for a reference to back this up. After some research from members of the committee several references were cited.
9-1-3g concerning a player occupying a marked lane space, and 4-45 concerning verticality were cited to support the instruction.

I need some convincing that either of these would support telling players they can only hold their arms straight up or down. What is your take on this and do these rules or any rules support this instruction?

Don't get me wrong here, I do not have a problem of preventative officiating and controlling the arm & hand contact along the lane line. I'm just not comfortable telling players they can only hold their arms straight up or down.