Rule SG4 a. Just states "No more than two (2) Balls may be in play at any one time" I cannot find any limits to possession by one robot.
The official VEX IQ Robotics Competition Question & Answer system has closed for this season.
Official Q&A: VEX IQ Robotics Competition 2024-2025: Rapid Relay
2014: SG4 and AG5: Can one Robot possess both balls?
Answered by committee
There are no rules preventing this, therefore it is legal.