[EricH]

If a word is not specifically defined (and "pinning" is not), the colloquial definition applies. In your proposed situation, the opposing robot is not pinned. They can leave at any time. You are simply blocking them from going sideways, which they may or may not have the ability or desire to do in the first place.

Now, if you were to then drive them into the field border so that they could not move, they would be pinned and you would have to let them go after 5 seconds.

Of note is that pinning is not specifically defined this year, and has been in the past. Also of note is that nobody has asked for a definition in Q&A.