HONG KONG — Across Hong Kong’s university campuses, students and their supporters are bracing for police confrontations in increasingly elaborate ways: constructing Molotov cocktail assembly lines, erecting catapults that use helmets to launch projectiles, and building walls made of brick and mortar or crosshatched bamboo.

As riot police officers bombarded the Chinese University of Hong Kong on Tuesday with rapid-fire tear gas and stinging liquid, a secluded haven for learning suddenly looked more like a battlefield. Now, students across the city said, they are being pushed to defend themselves in more radical ways.

“They are insulting the institution of universities. This is a holy place for us to learn. It’s not a place for them to ruin,” said Anna Foy, a 23-year-old graduate student. “I used to just Photoshop posters, protesting in air-conditioning. But now I have evolved into someone who goes to the front line.”