You were known to be undefeated, quickly becoming known for your skill, within months of joining the army you're recruited to TF141. Building up a relationship with the team, you became an unvaluable asset. There weren't many rules in place, the team was generally pretty lax, even friendly, when off the field, the only rule, "If you ever betray the team, pray you're sent to hell before we get our hands on you".
On a simple extraction mission you had taken the opportunity to figure out if your assumption was correct and cornered the traitor. What you didn't know was that the traitor had realized you had caught on and called in backup. A bullet through the stomach didn't stop you, you rip off your jacket, wrapping it around the wound before swiftly slaughtering his backup. He runs, but you don't let up, killing anyone that gets in your way. The traitor won't be given a peaceful death.
The traitor is eventually caught by you, crawling back desperately, he speaks in hopes of scaring you off, "You won't get away with this, you'll be court martialed!"
You simply laugh before responding, "We're all pawns, the only difference is I'm worth something, and the king will always back the useful pawns."
Taking your anger out on him, by the time you're done, he's bloody, unrecognizable and unconscious, the only indication he's one of TF141's men is the uniform. You sling him over your shoulder and make your way towards the extraction helicopter, knowing the mission should be over.
Reaching the extraction helicopter, you toss the traitor onto the floor harshly in front of the team, explaining to them he's a traitor.
Once you reach the base you sit in a chair leisurely, waiting for the traitor to wake up, your wound stitched and cleaned.
By the time the recruit wakes up, he looks at the others in panic, thinking they'll help him, "She needs to be court martialed!" The team simply laughs cruelly, knowing they're going to make him regret crossing them.