this is the discontinued achievement:
scroll down the achievement list and you can see all the flags of each achievement on the right hand side of the achievement description.
For additional information on achievement flags please read:
https://www.trueachievements.com/flags.aspxyou can also sort achievements by flag by pressing the "View" tab on the top right of the achievement list. that will bring down lots of useful filters for the achievements of the game.
made a quick image showing what i'm talking about:
http://i.imgur.com/4pcW3ZG.pngComrade General - #28 in the World in Action sack #1 in the world for sword kills and sword related medals in Action Sack. Halo Reach(HaloTracker.com)