I have never seen it in an amateur arranged boxing match. The form and power to deliver just isn't there. My wife had about 10 arranged matches over a twenty year time span. Actually, I'm in it for the fun, a knockout can be deadly serious. That's not for me.
In the early days (2003-2008 or so) of WMMA, and the pool of available fighters wasn't that deep, there were instances where one fighter would be trained on kicks, and the other was completely oblivious, not even trying to defend herself from a kick, and would almost literally walk right into a foot to the jaw.
Alanna Jones did that once, I think versus Holly Holm but don't remember.
That would often result in a total knockout.
That never struck me as very sportsmanlike, because the more-trained woman likely knew the unfair advantage she had. If you want to go ahead and score points with the judges by scoring kicks to your opponents hips or even her gut, go for it.
But, WTH, a kick to the jaw which you learned from Mr Niyagi on a trip to Okinawa against a novice opponent trying to make a name for herself a buy formula for 10-month old autistic daughter being babysat by her unreliable 52-year old stepmom? Really?