Hi, Jack. I only glance over the topics on the Island occasionally and I noticed this is a re-post of your question from an earlier thread so I sense that you are seeking to clarify the answer given earlier by Andre:
Andre147 wrote:As long as the line of the D is covering half of the cue ball, the cue ball is said to be "in hand".
Players can ask the referee if the cue ball is correctly placed in the D.
Of course, Andre as a certified Referee knows the Rules inside and out better than anybody else around here. You can be assured that yes, when the White is "in hand", it is perfectly within the Rules to place the White DIRECTLY onto the Green, Brown, or Yellow spots (assuming those spots are not occupied of course).
You may be parsing Andre's words beyond their original meaning which is likely the source of confusion. Yes, you are correct that if you place White directly on, say, Green spot, then GEOMETRICALLY speaking, more than half of the volume of the sphere is "outside" the confines of the "D". But that is not Andre's actual meaning. He is only stating one concept of how to think of this. What he means is to put it into a 2D viewpoint....as if you are an ant on the surface of the table. And you are looking at this giant White circle that is very near to a line on the ground. Is more than HALF of that circle on the left side or the right side of the line? It wouldn't matter if the ant is standing along the Baulk line or the very gradually curving (because the ant is tiny) semi-circle, the ant can only see one circle and one line from his perspective.
I prefer a different concept to explain this. In games that use "soft" spheres for balls with lines for boundaries, the Rules of those games may differ as ChengduFan explained for football or basketball. I would suggest to consider tennis with its "Hawkeye" technology. When the camera zooms in on the "smear" of the tennis ball print, all that matters is if even a tiny bit of that smear is touching the line. That is because the ball deforms as it touches the ground so there are many, many contact points with the ground. A snooker ball by contrast may be considered to be much more rigid and inelastic. I prefer to think of the White as if it were a globe with only one "North Pole" and one "South Pole" and obviously, the South Pole is that one exact point that is in contact with the baize. It is not a "smear" like the tennis ball. So the very simple Rule is that the South Pole of the White must fall within the confines of the lines of the "D" and precisely on the lines (as are the Yellow and Green spots) is defined as being within the confines of the "D".
I will even take this point a bit further to an obscure interpretation of this Rule. (I'm sure I have lost 98% of readership by this point anyway, so I will regale the few remaining hearty souls with a little known factoid.) Never seen on Professional Tournament tables because the cloth is always new and fresh, but a fairly common problem on Club tables with old and worn cloth, there may well be conflict between the Baulk spots and the lines of the "D". From regular re-spotting of the balls, "dimples" will always eventually be worn into the cloth so the ball will sort of wobble into that dimple like a gravity well when a ball is placed near it. Then, it is quite common to re-draw the lines of the "D" on an old cloth when it fades and the new "D" may not line up perfectly with the old "D". So to be clear, the actual, legal spot for a colour, any colour will be the dimple in the cloth if one exists. This may cause a contradiction when placing the White from in hand if it wobbles into, say, the Green dimple, and the South Pole of the White then APPEARS TO BE outside the confines of the "D". This would still be a legal placement because the White is ON the Green spot. The same logic is followed when determining if a spot is covered when replacing a colour, especially common around Pink and Black. If for example the Black spot APPEARS to be open when checked with a ball marker, but when the Black is attempted to re-spot and wobbles into the dimple touching a potentially interfering ball in the process, then the Black spot MUST be considered to be covered and Black then placed according to the Rules. If no other colour spot is available, then that Black would be placed near its spot but far enough away so that it is unaffected by the "gravity well" of that dimple. Again, you never see this professionally on telly, and usually at the club level where these problems actually occur, very few people know what to do in these situations.