A player legally pockets the 8 ball into a designated pocket, after all of that players object balls have been pocketed
The opposing player illegally pockets the 8 ball (e.g. before clearing all of that players object balls, does so on the same shot as the last such object ball, or the 8 falls into a pocket other than the one that was designated)
The opposing player knocks the 8 ball off the table.
The opposing player commits any foul, including scratching the cue ball into a pocket, or knocking it off the table, in the course of a shot that pockets the 8 ball. (As noted above, a scratch or other foul while shooting for the 8 ball is not a loss of the game if the 8 is not pocketed or jumped from the table.)