...does a lineout become a maul?
Skids, while your question was clear, there's a technical point that's very important to recognise. These are not mutually-exclusive phases; a maul can (and usually does) exist while the lineout is still going on. Only when the maul within the lineout moves fully beyond the line of touch, or outside the lateral lineout zone, or the ball emerges, does the lineout end. So stay on your guard for lineout offences as well as maul ones - particulary offsides by forwards behind the back foot, but beyond the 15m line. In terms of forming a maul within a lineout, the definition is the same as in open play: ball carrier plus one from each side, each bound as per the definition.
different here. Sack occurs between waist & shoulders
Assuming that the jumper was supported by one or more colleagues, what prevents the sacker then forming a maul? Presumably the sacker must grapple in a way that doesn't meet the definition of a bind?
I don't understand this.
As it takes a second attacker for a maul to form I don't see how any action by defenders, no matter their numbers, can be called an attempt to form a maul.
Rit, consider jumper with two supporters, no defender. There's clearly no maul. Now a defender tries to sack the jumper (who is still bound to his supporters) by grasping him firmly with one or both arms to wrestle him to ground. At the moment the arms grasp the ball carrier, the definition of a maul is met: ball carrier bound to at least one from each side. He's got two of his own, and one of the defenders as well. A maul now exists within the lineout.
Skids, this can be a minefield. Coaches coach the tactic without knowing the technicalities, and there is an expectation that this will be permitted. I received a scathing report from a L5 Group assessor for issuing a team offending YC for this offence in a L.8 game: I'd warned twice, bottled the first offence after the 2nd warning as being too inconsequential to card, and the non-offenders kicked for position. At the lineout, the serial offenders attempted a sack, failed and after about 3 metres of a driving maul by the attackers, the sacker achieved his objective of collapsing it. I carded him, and was roundly abused by the assessor for a lack of empathy. Damned if you do, damned if you don't. In retrospect, it's perhaps best until you reach the national leagues to allow coaches and teams to get away with what they all believe is legal.