Did anyone else see it this way?

[Dinger]

After reading this thread i noticed many people talking about "useing the arm for defense". can someone cite a rule that specifically says that the arm cannot be used for defense? its says another robot, or a tube that another robot posses cannot be grasped, and that an arm cannot be used to push another robot. However, i see no rule (and please correct me if i am wrong) about useing the arm to just get in the way. if other robots cannot make arm to arm contact legally it seems to me that putting your arm where the opposition wants to put thiers is a great and legal defensive manuver.
As far as i can see, from my interp of the rules the "Arm as defense" argument for a penalty seems void.