According to the One Punch Man Encyclopedia, Bang has a technique called "The abandonment" which allows him to increase his powers. Has he ever used this technique in the anime series or ovas?
The Wikia states:
And it's written clearly that:
Bang is seen utilizing this to prepare for his fight with Elder Centipede, so Bomb and Genos could escape with the unconscious heroes.
Which is right when King interferes the fight. He doesnt state the technique's name. But he powers up: