Running over a boulder foul

[Boltman]

The relevant rule (as you describe) is....

G38 ROBOTS may not control more than one (1) BOULDER at any time.
Violation: FOUL per extra BOULDER
Moving or positioning a BOULDER to gain advantage is considered
“control.”
Examples include, but are not limited to:
A. “carrying” (holding BOULDERS inside a ROBOT)
B. “herding” (intentionally pushing or impelling BOULDERS to a desired
location or direction)
C. “trapping” (holding one or more BOULDERS against a FIELD element
in an attempt to shield or guard them)
D. “launching” (shooting BOULDERS into the air, kicking across the
floor, or throwing in a forceful way)
Examples of interaction with BOULDERS that are not “control” include,
but are not limited to:
A. “bulldozing” (inadvertent contact with BOULDERS while in the path of
the ROBOT moving about the FIELD)
B. “deflecting” (being hit by a BOULDER that bounces into or off of a
ROBOT).
If a BOULDER becomes lodged in or on a ROBOT, it will be considered
controlled by the ROBOT. It is important to design your ROBOT so that
it is impossible to inadvertently or unintentionally control more than the
allowed maximum.


So any foul is likely because of above rule and if you question it then certainly ask the head referee at end of your match about it.