In 1938, the SEC imposed the uptick rule which disallowed short selling on a downtick. An uptick was required to short sell, the theory being that shorting downticks could create a cascading downward spiral.

Then, in 2007, the SEC dropped the uptick rule making it easier to short sell and create that cascading decline. Just ask Agent about MMs slapping the bids lower and lower with naked or shorted shares.

FINRA and SEC. What a pair.