Quick video explaining how to do the achievement. Pretty straight forward, just assign two settler's to the pads. One to the blue and One to the red, Once the second gets within a short distance of the pad, they will start a fight.
Run over to the Quitting bell siren and ring it, causing the settler's to come watch the fight, remember to power up the quitting bell also. Achievement should pop within a few seconds.
Note that if one of your settler's die in the fight somehow, It will effect your happiness rating for that settlement. (Based on tool-tip of Arena fight's)
Resource's required;
8 x Wood
32 x Steel
3 x Copper
2 x Circuitry
3 x Glass
Generator to provide 1 power rating to the quitting bell.
Hope this helps!