This action is very natural and almost follows as a corollary. This is the standard pinning action. if more calls are sold off at expiry, it creates a downward draft and if more puts are sold off, it creates an upward draft.
In Tesla calls certainly outnumber the puts, especially after weeks like what we just saw, creating a downward pressure. If the stock generally takes a dive during the week, the newly in the money puts get sold on Friday creating an upward pressure. All of this is a somewhat delicate dance and sometimes instead of converging into a pinning equilibrium, the stock takes off into a Friday close, going up or down. This is the exception though.
There is no point going into detail of why pinning happens, because others have gone into a good bit of detail around this. A good example is
here.
@generalenthu , thanks for engaging on the topic of whether pinning on Fridays is a systematic response of the market to options expirations or whether some manipulations are likely thrown into the equation. I'll refer to a market-induced pinning at a large nearby strike price as "auto-pin". I reproduce below the paragraph on pinning
from the article you cited:
Mechanism of Pinning
As the market approaches its close on expiration day, ITM call holders may sell their positions to lock in a profit. OMMs are obligated to buy these calls, but do not want to take on the price risk associated with holding the calls. Therefore, OMMs will hedge away this risk by short-selling the underlying stock into the close, thereby neutralizing price risk — the short stock position loses value as the long option position gains, protecting the OMM from price moves in a strategy known as delta hedging. Short selling tends to depress prices by increasing supply, so stock prices that were above the strike price are pressured downward toward the strike. The reverse situation occurs for put holders when stock prices are just below the strike near expiration: if the put holders sell their options, the OMM will neutralize price movements by buying underlying stocks, resulting in upward stock price pressure. The see-sawing of offsetting pressures is why stock prices get pinned to option strike prices at expiration.
As I read this article, the impression I'm left with is that auto-pinning occurs when we see substantial quantities of expiring calls and puts at a strike price near the stock's current price on expiration day. If the stock price moves in an upward direction above the strike price, then call buyers are likely to sell and take some return. The market makers who buy these soon to expire and slightly in the money call options don't want to be burned by losing their delta-neutrality, and so they short some shares in order to become delta-neutral again. I would concur that such short-selling by MMs would indeed place some downward pressure on the stock price, and it may account for some of the "whack the mole" effect in which we see any TSLA rallies above the prevailing strike price get sold off fairly quickly.
So far, so good with the theory of auto-pinning. Now let me introduce a few wrinkles to the theory.
The auto-pin theory relies upon puts sold at that strike price to balance negative movements in the stock price. If the price falls below the strike price of the puts and calls, put buyers will start selling some of those puts in order to recoup some of the money they have on the table, and MMs will buy the puts and then immediately buy some shares to compensate for the liability of holding those puts until close. The problem with TSLA last Friday was that even though there were over 4300 calls with strike of 1650, there were barely 100 puts at that strike, making the effect of put selling a non-event for market forces (see chart above). Some other force was needed to hold TSLA at 1650 and keep it there.
Another complication is that because of TSLA's volatility, there were multiple strike prices in play Friday afternoon. We had nearly double the quantity of 1600 calls vs. 1650 calls, and 1700 calls greatly exceeded 1650 calls in number, as well. Further, there were lots of intermediate priced calls, especially at 1630, 1640, and 1680. These too would influence the behavior of MMs as Friday got closer to expiration time on Friday. My point is that TSLA lacked the balance of puts vs. calls at 1650 on Friday, thus the balance of up and down forces keeping TSLA pinned at 1650 were not there in the traditional model. Further, the effects of all these nearby strike-prices complicates the situation and works against the theory that systematic forces were holding TSLA at 1650 on Friday afternoon.
Now, let me introduce another potential shortcoming of the auto-pin theory. Let's say that auto-pin is a thing, that it really works and it has a substantial effect upon the strike price. If this were the case, one could make money by manipulating the system on Fridays. Here's how. Notice that TSLA rose above 1680 in pre-market trading (see chart below). If you were a hedge fund with lots of money and really didn't care whether TSLA rose or fell on Friday, you could nonetheless make money by shorting the stock to bring the price down from 1680 to a more sustainable 1650. The auto-pin would then take over and work to hold TSLA near 1650. This would allow you to slowly and methodically cover your morning shorting below 1650 because the auto-pin mechanism would be covering your back during the cover period.
My overall impression is that you brought up a mechanism that can indeed result in auto-pin with the right circumstances. I would question how often you would get the right circumstances with TSLA, however, because the volatility of the stock results in calls and puts being located quite some distance from each other, there not being just one dominant price where calls and puts are located, and the opportunity for manipulators to use any auto-pin mechanism as part of their manipulations of the auto-pin mechanism had some real strength to it. Overall, I think because of the volatility of TSLA, the high percentage of trading that is done via options vs. shares in this stock vs. others, and the track record of some very flagrant manipulations having happened in the past, I would say that TSLA is a unique stock that requires a unique understanding. Nonetheless, the explanation you linked to is indeed helpful for understanding one of the many mechanisms that is affecting TSLA's price, and so I appreciate your bringing that mechanism to our attention.