Can you explain the sack of doorknobs? I'm a bit behind in idioms I guess.

It's an old school Mafia beat down tactic. It's also done in the military and in prisons, where if one person screws it up for everyone else, they are beaten with a towel/ sock/ pillowcase/ sack full of heavy objects, some of the most common being doorknobs, padlocks, bars of soap, cans of soda, etc. The main reference to doorknobs as the objects in the sack seems to be two-fold. First, it's mainly attributed to the Simpsons, and secondly, someone acting dumb, such as the Cryptarch, was often referred to as being "dumber than a doorknob." This game is full of hidden pop-culture references, such as the Hand Cannon weapon type, and so, it seems, are the news articles.