Opinions On This Half Penny Please

Wow...interesting! Definitely outside my experience on Australian coins, but at first glance I note how consistent the mint luster crosses the rim/denticles area in question, and the very clean transition from denticle detail to the dented region. My take is this happened during the strike somehow--unsure though. A real telling feature might be the rim, and whether any metal is pushed outside the circumference of the coin? If the damage happened post-mint, it would likely change the shape of the rim. If it happened during the strike, the collar would contain the spread--I believe. From your shots, I don't see evidence of a spread.

One more thought after re-reading NancyC's post, I note how there's rim weakness opposite the larger mark just below LF...P. That might suggest an incomplete/damaged/clipped planchet prior to strike--just a guess!

What I noticed first was the diminishing size if the dentiles from very large at the bottom of the coin and going around to reach the weird area the dentiles get smaller and how normal the dentiles are inside the affected area .

Well I've never seen anything like that. I'm leaning toward faulty/damaged planchet rather than post mint damage. That sort of ding would have lead to deformation of the coin which I dont see. It should have lead to some damage of the obverse which I also dont see. I do see some weakness in the obverse opposite (which would happen because there would be 'give' in the metal because of the damage). All of this is only an opinion though, because as I said, never seen it before :)