The most common and most likely answer to this crossword clue is the 7 letter word LOCKING
I've seen this crossword clue in The Guardian
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More clues leading to the result LOCKING
Buddy explains!

The straight part
We know that "Jamming" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case jamming = locking.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LOCKING mean?
LOCKING verb- To become fastened in place.
- To fasten with a lock.
- To be capable of becoming fastened in place.
- To intertwine or dovetail.
- (break dancing) To freeze one's body or a part thereof in place.
- To furnish (a canal) with locks.
- To raise or lower (a boat) in a lock.
- To seize (e.g. the sword arm of an antagonist) by turning the left arm around it, to disarm him.
- To modify (a thread) so that users cannot make new posts in it.
- (WMF jargon) To prevent a page from being edited by other users.
- The act by which something is locked.
- The use of a lock or a mutex to restrict access to a part of the code to at most one process.