They were actually instituted after major drops in 1987 and 1989. More recently they are being used to limit the impact of programmed trading, since computer programs can be set to automatically sell holdings when the price drops a certain percentage. Trading curbs are set by the exchanges with a percentage and time - for example, a 10% drop on the NY stock exchange will result in an hour long curb.

You would have to quote the law exactly or give a link to where it can be found. Anti-shorting regulations have come and gone, or are you referring to some anti-fraud regulation regarding shorting?

We could guess and do a lot of typing, but the question doesn't deserve it. You are mixing terms and its doubtful you know what a "crash" is if you refer to 2009.

What definitions are you using for "crash" and "circuit breaker?" Which stocks? There isn't enough information given to answer the question, or figure out what the question is about, specifically, or which context.

I noticed that stocks that have experience a drastic drop in price during a short period of time gets put on a regulatory circuit breaker, where you cannot short the stock.

I was wondering is this a new rule that was added after the most recent stock market crash in 2009. Or has this anti-shorting regulatory circuit breaker always been there?