so this happened to me yesterday..
winger crosses the try line simultaneously being tackled by two defenders. the players hit the ground in goal, ... during the small time that one would allow the ball-carrier to attempt to ground the ball immediately (a second or two I guess?) the momentum and his wriggle carries his foot into touch in goal.
The tacklers had a good grip on the ball carrier and ball he doesn't manage ground it. Blow the whistle.
Held up, 5m scrum... or touch in goal, 22m drop out?