This is why the rule should be benefit of the doubt goes to the shooter. No replay would have been required and Marcel could have overruled.
Either that or just make them shoot away from it like APA, lol.
The official APA rules don't actually require shooting at an angle, but they do suggest that or jacking up to 30 degrees elevation to reduce the chance of a double hit on a close ball. The APA seems to be the same as the WPA for a frozen ball.
As Bob stated, the APA rule for a double hit mirrors the WPA rule for a double hit. Here's the APA definition of a double hit:
Double-Hit: An illegal shot involving the tip of the cue stick coming into contact with the cue ball twice during the execution of a single shot. This foul may occur through double clutching the cue ball, or in situations where the cue ball is nearly frozen to the object ball or rail. In the latter case, the double-hit often occurs due to the difficulty in moving the stick away from the shot quickly enough to avoid the cue ball rebounding back into the stick. In general, the shooter can lessen the likelihood of committing this type of foul by hitting the cue ball into the object ball or rail at an angle, or by elevating the butt of the cue about 30 degrees. This does not guarantee that a foul will be avoided; however, it cuts down the length of the follow through, which is the principal cause of a double-hit.
The APA takes a bit of a different stance on push shots. Here's their definition of a push shot:
Push Shot: A shot in which the cue ball is frozen to the object ball, and the shooter keeps the tip of the cue on the cue ball while pushing through the shot. Push shots are not fouls, but players who repeatedly guide the cue ball with force through object balls that are frozen to the cue ball, using a level cue and long follow through, may be subject to a sportsmanship penalty. In general, you can lessen the chance of being accused of shooting a push shot by hitting the cue ball into the object ball at an angle, or by elevating the butt of your cue about 30 degrees.
The APA has a few situations where you'd think rules apply, but they are not technically "fouls" in APA, just a sportsmanship violation. Most often those are done unknowingly, by less experienced shooters, and it affords an opportunity to explain that after the shot, but that doesn't always happen.