This answer is probably referring to the practice of tapping a sword on the shoulders of someone who is being knighted, for example Sir Bruce Forsyth here. The fencing company Leon Paul wrote a letter to the Palace asking if the royal family had fenced at school, and were told it was a private matter, so it's possible that Elizabeth fenced when she was younger, but the makers of trivial pursuit would have no way of knowing that. There are no recorded events where Elizabeth II attacked somebody with a sword outside of these two possibilites.