Ranger Takedown

Ranger Takedown is an Unarmed perk

Obtaining
It's acquired by being successful in a Speech challenge with Ranger Andy after he tells you about his multiple leg injuries. It can also be acquired by completing an unmarked quest which requires checking up on Ranger Station Charlie and telling him what happened there.

Effects
This perk grants the ability to do a special attack by moving backward and doing a power attack. If done properly, the character will do a special move that knocks the enemy back and down, incapacitating them for a few seconds.

Bugs

 * The attack may stop working altogether at random moments. This may be fixed by restarting the console/game.
 * Sometimes the knockdown effect does not trigger, though unlike the above bug, successive attempts may succeed.
 * When you learn the attack: After a successful Speech check and dialogue ends, you will get a message box stating you have learned the Ranger Takedown. After acknowledging the message, the game will fade out/fade in and upon initiating dialogue with Ranger Andy, you will get the message box a second time and upon acknowledgment, the game will freeze. On PS3 the PS button will still go to the X-media bar, allowing you to quit the game from there rather than shutting off the whole console (also on PC). You could avoid this bug by asking directly what happened to his leg, passing the Speech check, exiting the dialogue, and re-initiating the dialogue OR following the dialogue branch WITHOUT asking about his leg and exiting the dialogue. This bug may have something to do with Ranger Andy requesting you to check on Ranger Station Charlie the first time you exit dialogue with him normally. Since the Speech check automatically ends dialogue doing it the first time you speak with him may mess with the game's scripting, causing the freeze.
 * When using this on dead characters repeatedly, it can complete the challenge Knocked Up.
 * When performing a Ranger Takedown on an enemy in a corner or similarly clipped area while the enemy has already been knocked down, the enemy will sometimes get stuck briefly, or on rarer occasions, they may get launched across the room. This usually happens indoors and has been heavily tested with ED-E and Boone.
 * When performing the Ranger Takedown (mostly in 3rd person mode) the game might freeze.
 * When used on companions, it can complete the challenge Knocked Up.