Stocks usually fall during Powell's news conference, and Cramer thinks it may happen again

Stocks tend to fall slightly when Federal Reserve Chairman Jerome Powell speaks during his post-decision news conferences, history shows. And CNBC's Jim Cramer believes we could be setting up for a similar performance, and possibly even worse.

Bespoke Investment Group looked at the intraday data and found the S&P 500 typically is higher going into the 2:30 p.m. ET news conference, but then, on average, turns lower when Powell's briefing begins. After the move down, the benchmark ends Powell press conference days lower by 2 basis points, according to Bespoke. (1 basis point is 0.01%.)

"Powell taking the podium has been the equivalent of 'last call' at a bar," the firm said in a note.