Good question, but I haven't seen any. The core concept is that there are a bunch of folks that more or less promise to either post bids (promises to buy) or o

Good question, but I haven't seen any. The core concept is that there are a bunch of folks that more or less promise to either post bids (promises to buy) or offers (promises to sell) continuously, and for that promise they (sometimes) get special treatment as 'market makers.' In an orderly market, there are both bids and offers for every instrument. A market maker (or really any market participant) desire to participate in the market is a function of a) the rest of their portfolio (whether they are net 'long' or net 'short') and b) their expectations of when and at what price they can unwind the trade if they get 'hit' on their bid (aka someone sells to them at their posted price) or 'lifted' on their offer (aka someone buys from them). When markets are moving 5-6% an hour, it becomes almost impossible to have any certainty on a) what the rest of your portfolio really looks like and b) when and at what price you might be able to unwind a particular trade. This results in market makers (and HFT, and other market participants) basically exiting the market. When people say the 'bid-offer spread is wide' this is usually what they are referring to. All the usual players basically take a step back and say 'too rich for my blood' and then you have wide markets, and 'risk premiums' for assets all over the place. Circuit breakers are an attempt to slow time down to give people a chance to understand their portfolios better, and hence return to the market. Wide bid-offers represent highly profitable market opportunities, if the market is orderly. When it's not, you get stuff like an ETF on US government bonds trading as a steep discount to the 'intrinsic value' of the underlying bond portfolio. Aka chaos. https://ycharts.com/companies/TLT/discount_or_premium_to_nav https://ycharts.com/companies/TLT/discount_or_premium_to_nav