Recently booked HA one way close-in to the departure date. Price dropped and received $50 credit without request or any interaction on my part.
I do believe that the booking page has to specifically state that price protection is applicable. There's also a notice in the confirmation email.

I also noticed that more restrictive search (e.g., nonstop only, no basic) would result in price protection being removed from the search results.
I recommend trying your search without as many filters to see if price protection is offered prior to booking.