Is this a legal shot?

[Bob Jewett]

I can't picture that froze bank being a legal hit, Bob.
Paul Bruesloff showed me that shot in Detroit a long time ago...he said he could prove
it was a bad hit....he cleaned the cue....and breathed on it to fog it up....
...then he made the bank and showed six or seven different chalk marks on the cue ball.
Paul said he didn't think anybody could make the shot and leave one chalk mark. ...

That's an interesting observation. Maybe a lower hit is required to avoid the sliding/miscuing action. And a lighter cue.

 

[Los Gatos Taki]

Rules of one pocket indicates that is ok to take an deliberate foul by touching the cue ball and failing to contact a rail or pocket a ball. HOWEVER, the rules state that to do so, a player MUST make contact by using a LEGAL STROKE. Just spotting a ball or tapping the top of the cue is not using a legal stroke to make contact. This foul falls under a different type of illegal shot foul penalty description and could also be called for unsportsmanship.
To my understanding