Substitutes were responsible for yesterday’s market selloff.

Remember back in school when you had substitute teachers? They were standing in for the real deal, no offense to substitutes.  But did you maybe take them a little less seriously than the home room teacher?

The market is saturated with substitutes. The difference between stocks and the home room back in grammar school is nobody knows the difference.

If shares are borrowed they look the same to the market as shares that are not borrowed.  If you use a credit card, the money is the same to the merchant from whom you just bought dinner or a summer outfit. But it’s a substitute for cash you may or may not have (a key statistic on consumption trends).

Apply to borrowed stock. The average Russell 1000 stock trades $235 million of stock daily, and in the past 50 trading days 46%, or $108 million, came from borrowed shares. The Russell 1000 represents over 90% of market capitalization and volume. Almost half of it is a substitute.

Why does it matter?  Suppose half the fans in the stands at an athletic event were proxies, cardboard cutouts that bought an option to attend a game but were there only in the form of a Fathead, a simulacrum.

The stadium would appear to be full but think of the distortions in player salaries, costs of advertisement, ticket prices.  If all the stand-ins vanished and we saw the bleachers were half-empty, what effect would it have on market behavior?

Shorting is the biggest substitute in the stock market but hardly the only one.  Options – rights to buy shares – are substitutes. When you buy call options you pay a fee for the right to become future demand for shares of stock.  Your demand becomes part of the audience, part of the way the market is priced.

But your demand is a Fathead, a representation that may not take on greater dimension. Picture this:  Suppose you were able to buy a chit – a coupon – that would increase in value if kitchen remodels were on the rise.

Your Kitchen Chit would appreciate if people were buying stoves, fridges, countertops, custom cabinets.  Now imagine that so many people wanted to invest in the growth of kitchen remodels that Kitchen Chits were created in exchange for other things, such as cash or stocks.

What’s the problem here?  People believe Kitchen Chits reflect growth in kitchen remodels. If they’re backed instead by something else, there’s distortion.  And buying and selling Kitchen Chits becomes an end unto itself as investors lose sight of what’s real and focus on the substitute.

It happens with stocks. Every month options expire that reflect substitutes. This kitchen-chit business is so big that by our measures it was over 19% of market volume in the Russell 1000 the past five days during April options-expirations.

It distorts the market.  Take CAT.  Caterpillar had big earnings. The stock was way up pre-market, the whole market too, trading up on futures – SUBSTITUTES – 150 points as measured by the Dow Jones Industrial Average.

But yesterday was Counterparty Tuesday, the day each month when those underwriting substitutes like options, futures, swaps, balance their books.  Suppose they had CAT shares to back new options on CAT, and they bid up rights in the premarket in anticipation of strong demand.

The market opened and nobody showed up at the cash register. All the parties expecting to square books in CAT by selling future rights to shares at a profit instead cut prices on substitutes and then dumped what real product they had.  CAT plunged.

Extrapolate across stocks. It’s the problem with a market stuffed full of substitutes. Yesterday the substitutes didn’t show up to teach the class. The market discovered on a single day that when substitutes are backed out, there’s not nearly so much real demand as substitutes imply.

Substitution distorts realistic expectations about risk and reward. It’s too late to change the calculus. The next best thing is measuring substitutes so as not to confuse the fans of stocks with the Fatheads.