From The New York Times:

The convention floor turned into a scene of momentary discord and boisterous dissent on Monday. Those who were opposing Donald J. Trump broke into booming jeers and chants of “Roll call vote! Roll call vote!” in an attempt to demand a vote by all 2,472 delegates on a procedural motion that is required before the convention can formally get underway.

Their hope was that by starting a lengthy process so late in the day — just a few hours before the convention’s prime-time programming was set to begin — they could embarrass Mr. Trump by delaying the convention’s opening speakers.

Delegates who opposed them appeared to have the advantage. And they responded with their own noisy shouts of “USA! USA!”