Below the timer is the Guard Libra gauge. If you block attacks, the gauge will fill towards your direction. Once it has filled up and you are attacked again, your guard will be broken and you will be stunned for a brief period of time. This is what it's referred to as a barrier crush.
To earn this achievement, you will need to barrier crush opponents 5 times, this is cumulative and doesn't have to be done in one match.
If you have a wired controller. You can set yourself as Player 1 (Controller) and set the keyboard as Player 2 in versus mode. Choose any characters you want. Once the game loads up, simply block with Player 2 (Holding the directional key away from your opponent) and using your main account simply attack the guarding opponent. As you attack him the guage will fill in his direction and eventually his guard will be broken. Simply repeat 4 more times.
If you do not have a wired controller. I suggest changing the difficult to "Hell" and playing arcade mode with Jin Kisaragi. Simply use his Ice Car move (QCB + ) and the enemy will keep blocking the attack. Eventually their guard will break.