The remaining thug saw that eight of his fellows had died and the boss had jumped into the sea to escape. At this point, he had no will to fight and wanted to jump into the sea to escape as well.
He and Helen Wilson were evenly matched. At first, he let Helen sneak attack him and suffered some injuries, always on the defensive. Now, without the will to fight, he was at a disadvantage. Just as he wanted to turn around and jump into the sea, Helen swept his thigh with a whip kick, making him fall onto the deck with a thud. Helen bent her right leg and knelt on John's back, grabbing the thug's right hand and twisting it hard, rendering him completely powerless to struggle.
Killing isn't her thing, but doing something like this, Helen is quite adept.