[EricH]

Originally Posted by apalrd

and if you are ever in the opposing alley it's a penalty under [G28], even if you were collecting balls)

Palardy, I don't see anything in [G28] that bars entry to the Key or Alley (Bridge is covered elsewhere).

[G28]
Robots may not touch an opponent Robot in contact with its Key, Alley, or Bridge.
Violation: Foul; Technical-Foul for purposeful, consequential contact.

And neither does the GDC:

Game - The Game » Robot-Robot Interaction » G28
Q. Can a robot (that is not in violation of G28) touch or enter the key or alley of the other alliance?
A. Yes