A Guard Break is when you attack a guarding opponent enough in a short period of time that their guard breaks, leaving them open and vulnerable to attack. This is not to be confused with a guard crush attack (hold :triangle), which is an attack that automatically breaks an opponent's guard on contact. To earn this trophy you have to attack a blocking opponent enough times to have their guard break. This is shown in the game by a faint, red glass shattering behind your opponent. Do this 5 times to earn this trophy.
From
https://www.playstationtrophies.org/game/jojo-eyes-of-heaven...