[pashamur]

Big crashes (and fast-drop bottoms) happen not because of panic selling, but because of forced selling (covering margin calls, getting liquidated, etc). Panic selling usually leads to slow grind downs.

Shorts usually cover once the rebound starts, not when things are free-falling (their trailing stops get triggered, etc)

[qeternity]

No. Again, like short selling, you misunderstand the relative ratios of beta length vs. everything else. Smaller moves, at the money, occur because of this or in single names in multi SD moves (a la Archegos). The prevalence of vol control strats today means we also see these sorts of moves around key index gamma levels, but we're talking 100bps travel.

Mar'20, 2008, etc - these did not happen because guys were getting margined. These happened because because were panic selling huge amounts of length.