The opposition began their attack, and the government troops hiding had to return fire; otherwise, their blockade would be immediately overrun.
Gao Yang started 'calling roll' with bullets, mercilessly shooting anyone daring enough to expose themselves and fire.
The government forces were far stronger than the opposition's untrained militia, but strength is relative. They couldn't even begin to suppress Gao Yang; they could only wait desperately for the bullets to come.
A sniper puts too much psychological pressure on people; the fear of an unforeseen bullet is enough to make someone collapse, especially for the government troops who had no backup and no hope of victory. Eventually, they broke.