When one or more of your object balls remain on the pool table, it is a standard foul to use the 8 ball as the first ball in a combination shot.
If a player does this, they have committed the standard foul of striking the "wrong ball first". Standard fouls in eight ball pool result in the opponent taking the cue ball in-hand from anywhere on the playing surface.
Here is a summary of how the rules of 8 ball apply to this situation, and below this are the detailed World Pool-Billiard Association ("WPA") rules which apply.
- Players must always ensure that the cue ball first contacts a ball from the shooting player's group. The 8 ball isn't part of either group (solids, stripes).
- Players can not "call" the 8 ball until all of the object balls from their group have been pocketed.
- Contacting the wrong ball first is a "standard foul".
- Any balls pocketed on the foul shot remain pocketed.
- A "standard foul" results in the opponent taking ball in hand, anywhere on the table.
Note that if the 8 ball is incidentally pocketed (e.g. by mistake), the shooting player loses the rack
Here are the relevant WPA rules which relate to this scenario (emphasis ours):
3.9 Standard Fouls (8 Ball)
If the shooter commits a foul, play passes to his opponent. The cue ball is in hand, and the incoming player may place it anywhere on the playing surface. (See 1.5 Cue Ball in Hand.)
The following are standard fouls at eight ball:
- (6.2) Wrong Ball First - The first ball contacted by the cue ball on each shot must belong to the shooter’s group, except when the table is open. (See 3.4 Open Table / Choosing Groups).
The "wrong ball first" foul is further explained in section 6.2:
6.2 Wrong Ball First
In those games which require the first object ball struck to be a particular ball or one of a group of balls, it is a foul for the cue ball to first contact any other ball.
This also applies in an open-table scenario after a break shot.
3.4 Open Table / Choosing Groups (8 Ball)
Before groups are determined, the table is said to be “open,” and before each shot, the shooter must call his intended ball. If the shooter legally pockets his called ball, the corresponding group becomes his, and his opponent is assigned the other group. If he fails to legally pocket his called ball, the table remains open and play passes to the other player. When the table is "open", any object ball may be struck first except the eight ball.
Also note that all of the above only applies if the 8 ball isn't accidentally pocketed.
If the 8 ball is accidentally pocketed during the scenario in question, then the shooting player automatically loses the rack.
Here's the WPA rule listing "serious fouls":
3.8 Losing the Rack (8 Ball)
The shooter loses if he
- (a) pockets the eight ball and fouls.;
- (b) pockets the eight ball before his group is cleared;
- (c) pockets the eight ball in an uncalled pocket; or
- (d) drives the eight ball off the table.
These do not apply to the break shot. (See 3.3 Break Shot.)
Rule 3.10 shows that the penalty for a serious foul is the loss of rack for the shooting player:
3.10 Serious Fouls (8 Ball)
The fouls listed under 3.8 Losing the Rack are penalized by the loss of the current rack. [...]