They stand in a row.
to break from the procession―fall out of the line
to fall out of the line―drop out of the line―(にわかになら)―break from the procession
to break through a procession
列に並ぶ.
列をなして.
to break up the ranks
(行列なら) to cross a procession―(兵隊の列なら)―break through the ranks
to lead the procession―lead the van