In the following situation would your robot be “pinning” the other robot?
Let’s assume that you’re facing the opposing robot and the robot is 1 foot from the side of the field and is 1 foot from the front of your robot. The opposing robot robot is facing towards its goal at one end of the field. (Therefore the opposing robot could easily escape the pin just by driving either forwards or backwards).
The only rule I could find talking about pinning is <G31>:
"An ALLIANCE may not pin an opponent ROBOT for more than five (5) seconds. A ROBOT will be considered pinned until the ROBOTS have separated by at least six (6) ft. The pinning ROBOT(S) must then wait for at least three (3) seconds before attempting to pin the same ROBOT again. Pinning is transitory through other objects. "
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.