Tourney: Cambridge Indoor Open – 26/27th February

Cambridge, I just read the rules, can you clarify something for me:

If the ball is shuffled into the goal by the offensive team, the defensive team gets possession of the ball.
How are you defining possession in this case? Is it enough for the ball to touch a defensive players mallet in any form? Do they have to have possession for a certain amount of time? Does the offensive team have to back off?

What I'm asking is what the offensive team are obliged to do in that situation.