The organizers of the
2016 STEMley Cup Championship are considering several modifications to the Stronghold game including freezing of the moats and this one:
"5. The evolution of the BOULDER...
the CANNONBALL: one red and one blue CANNONBALL (ie. coloured BOULDER) start the match behind their respective alliance walls and may be introduced to the field by the HUMAN PLAYER only in the last twenty seconds of the MATCH. CANNONBALLS, being more destructive than ye BOULDERS of olde, are worth double the value of a regular gray BOULDER when scored in a tower GOAL (ie. ten points in the HIGH GOAL and two TOWER STRENGTH POINTS, four points in the LOW GOAL and two TOWER STRENGTH POINTS)."