So, am I missing something here? (which is probable).
Red attacking into Blue in goal:
1. Red #11 enters in goal carrying the ball
2. Red #11 knocks it forward
3. Ref: "Advantage"
4.a Blue grounds the ball
5.a Ref: "Advantage Over. PeeP. 22 DO"
4.b Red grounds the ball
5.b Ref: "PeeP. No advantage, KO Red, Scrum Blue on the 5m"
4.c. Ball goes over DBL / TIG
5.c Ref: "Advantage Over. PeeP. 22 DO"
Same logic goes for a grubber (question is: who brought the ball in in-goal?)
And it's too fast to call the "advantage", don't just sell your decision based on that.
Keep It Stupid Simple
epper:
Now, just in case one is not convinced you can do that (basically: play advantage after a knock-on by attacking team in defending team's in-goal, consider this:
4.d Blue picks up the ball, run the whole length of the pitch in a "try from the end of the earth" movement to score as the hooter goes and win the game
5.d Ref: __________________ (your call)
Pierre.