[Procolsaurus]

The following criteria define POSSESSION :
A) “carrying” (moving while supporting BALLS in or on the ROBOT),
B) “herding” (repeated pushing or bumping),
C) “launching” (impelling BALLS to a desired location or direction), and
D) “trapping” (overt isolation or holding one or more BALLS against a FIELD element or ROBOT in an attempt to shield them).
Violation: TECHNICAL FOUL per instance.

Immobile robots are incapable of A and B, and I can't really see how D can occur. LAUNCHING would be very easy to accomplish, a robot whose top formed a ramp could passively sit near the human player and receive the ball and allow the ball to roll off in a desired direction.