if sprites in scanline are 8, what does it mean "drop" to the next scanline?
the next scanline will start evaluating in range sprite 0, i think, thats why flickering effects when > 8 sprite are in the same scanline?
Sprite evaluation is done one scanline before they are actually drawn on screen (1st part: sprite Y coordinate evaluation, 2nd part: reading a maximum of 8 sprite tiles).
If more than 8 sprites have been found in the 1st part, the sprite overflow bit will be set, and the game will decide on whether to make the sprites flicker or not, by polling the sprite overflow bit and then rotating the sprite RAM. Sprite flickering is not a hardware effect.
I don't think many games use the overflow bit of $2002 to determine whether to rotate sprite order; I think they just rotate it anyway. And remember that the sprite overflow bit in $2002 is not as simple as "more than 8 sprites on a scanline":
NESdevWiki page. I had to play around with this on my NES to be sure I understood it correctly.