Eye for an Eye (Fallout: New Vegas)

Eye for an Eye is a side quest

Detailed walkthrough
After discovering Cottonwood Cove, go visit First Sergeant Astor (who patrols around Camp Searchlight). One can initiate a dialogue about Cottonwood Cove and Astor asks the player character to travel to Cottonwood Cove, collect some intelligence on Legion troop movements, raids, and plant a bug in their radio.
 * The Legion raid intel is in a filing cabinet to the left of buggable radio (left while looking at the radio) on the first floor Command HQ building. The intel on Legion troop movements is in the desk on the second floor. Because taking both intel documents is considered stealing, this will give you negative karma.
 * Alternatively, the Courier can expose the plot to Aurelius of Phoenix, and give him the NCR bug (this will give Legion Fame). Aurelius will in turn give them the Old Legion paperwork, Old Legion patrol notes, and Old Legion raid plans. If these pieces of false intelligence are given to Astor, he thanks you, and the quest concludes, with you receiving 500 XP, 150 caps, and Legion fame.

If the Courier returns to Astor with the real intelligence and plants the bug, 500 XP will be gained and the Courier gains an additional option to wipe out all Legion forces from Cottonwood Cove. This provides NCR fame, 250 caps, Legion infamy (if they spot the Courier in the act) and 1000 XP. When one receives the option to wipe out the Legion fort, Astor calls them "crazy" but believes they can pull it off.

To get the most fame with the NCR, locate the red truck hanging precariously off the cliff at Cottonwood overlook over the Legion camp. The Courier's Geiger counter will show radiation leaking from the truck when you get close. Go to the back of the truck, and select the door. The option to open the door becomes available (50 lockpick required), dropping several radioactive barrels into the camp, effectively killing the Legion the same way they killed the NCR forces at Camp Searchlight. Astor is quite pleased with this outcome.

It is best to wait for all the barrels to fall into the camp before fast-traveling to talk to Astor. If one opens up the truck but fast-travels to Astor too soon, then the game doesn't realize the legionaries were killed using the radioactive waste.

Bugs

 * Sometimes dropping the radioactive barrels will not kill all the legionaries. They will remain standing in front of the barrels without ever succumbing to the radiation. Four legionaries line up at the base of the cliff while the barrels roll right through them. However, the objective is still marked as complete in spite of the fact that the survivors can still be killed, targeted through V.A.T.S., and otherwise interacted with.
 * The truck door isn't always locked, making the quest much easier.