[kuraikou]

The manual says that "An ALLIANCE may not POSSESS their opponent’s BALLS. 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."
So I think that blocking is not allowed, but it is iffy.