While pressing the R2 attack button, move the left stick forward.
A visceral attack is a good tactic when facing the bigger enemies in Bloodborne. To pull this off, wait until the enemy attack and then parry the attack with a gunshot. Then follow it up with a R1 attack.
Learning from your experiences are a big part of Bloodborne. Here I got mobbed by 5 guys and a boobytrap. I then returned to get my revenge in the laziest way possible.