At what point does scoring on a mobile goal with a lady brown while already in control of a mobile goal become a violation of SG6?
Please review the Q&A Usage Guidelines before posting, specifically point 2, "Read and search existing Q&As before posting.” We believe our answer to Scenario B in Q&A 2520 addresses your question.
That said, we can expand a little bit on our guidance from that question. Scoring a Ring on a Mobile Goal while in Possession of another Mobile Goal isn't automatically an <SG6> Violation, but if a Robot continues to hold onto the Ring after it's clearly Scored on the Mobile Goal they risk an <SG6> Violation if the Robot's actions would then move the 2nd Mobile Goal (and the Robot that's Possessing it) in a preferred direction or prevent the Robot or Mobile Goal from moving.
Any interaction with a Mobile Goal while already in Possession of another Mobile Goal is a dangerous strategy, with an inherent risk that a judgment call by the Head Referee may not be in your favor. To quote a head referee from this season, "If you have a mobile goal, pretend you're the Titanic and other mobile goals on the field are icebergs. If you touch one, it could sink you."