**10G. Accidental release of piece. **
A player who deliberately touches a piece and then accidentally releases it on an unintended but legal square is required to leave it on that square.
Is the point no one knows what was intended and releasing the piece is observable? A friend of mine asked, why not just fix the accident?
There were related posts over the years but I didn’t find the distinction “clock move” versus “touch move” that seems to be the bottom line. Is it?
Keep reading, Mike. 
I found this:
Move takeback -- part 2 - #7 by timjust mentioned clock vs touch.
The piece was touched in a way that looked like an attempt to move (grabbed in this case) and then released on a legal square. No need to try to figure out whether or not an accident occurred.
Note that released on a legal square also means the piece must be positioned legally (standing up, not on its side).
Right, it makes no sense to judge motivation. Simply observe the moves. Then why is “accidentally” part of a rule?
Two reasons I can think of, but I don’t know if either was the motivation:
By analogy to rule 10E, “Accidental touch of piece,” where the intent is the key point of inquiry; and/or
To make it clear that intent is not relevant for this rule.
“Accidentally” is part of the rule to emphasize that even when a player says an accident occurs then the release on a legal square still counts. Since it is the same result whether an accident occurred or not, you don’t have to try to figure out whether it was a real accident or somebody saying that it was an accident after realizing it is an error.
That is the same reason 10B says “in a manner that may reasonably be interpreted as the beginning of a move”. When somebody grabs a Bishop on b2 and moves to f4, while another Bishop is also on c2, the grab of the Bishop on b2 triggers touch move even though it is apparently an accidental grab of he wrong bishop. That eliminates a person intending to play Bb2-a3, realizing after picking it up that Bc2-f5 is stronger, playing Bb2-f5 in an attempt to claim the intentional impulsive grab of the b2 Bishop was an accident and forcing a TD to try to figure out whether that claim is valid (essentially saying whether or not the player seems to be lying).
Both situations say “what was done, was done” and the player’s truthfulness or lack thereof is irrelevant and unnecessary to decide upon.
Judgement calls come in when players disagree on whether or not a piece was grabbed (in over four decades of directing I’ve seen occasional false claims both directions) and whether or not a piece was inadvertently brushed while reaching for another piece rather than actually touched (I’ve seen honestly erroneous claims in both directions).
My wife has an essential tremor that runs in her family, she loses precise control of her hands when grabbing small objects like chess pieces all the time, and frequently drops them. So I’m very aware of the potential for accidentally touching or dropping a piece.
These are very helpful. I supposed I should have narrowed down my question about “accidental” to 10G where it doesn’t matter. I like the what was done was done. Thanks all.
I was at a tournament where and older gentleman (who might have had Parkinson’s) had a bishop on b2 that was able to take on g7 further attacking a rook on h8 - he dropped his bishop on f6, got frustrated for a second, and then pushed the B to g7 replacing the pawn. No question in anyone’s mind he always intended to take on g7 and only dropped the piece due to a physical disability. The opponent called the TD … the Bf6 stood – that must have been a very satisfying win (no prize at stake)