Wizards star Bradley Beal just went off on Donald Trump ... trashing POTUS in a big way ... and essentially teasing more protests when the NBA season starts. 

Beal used the mic at Wizards media day to call Trump a "clown" and voice his displeasure with everything the President is doing ... from race issues to Puerto Rico to Twitter. 

"I disagree with what he's doing. I disagree with his thoughts. Hopefully as a nation we can come together better and really see things through the perspective of the people really going through it."

The NBA season begins on Oct. 17 -- and with several prominent NBA players from LeBron to KD to Steph to Beal speaking out against Trump, it'll be interesting to see if they demonstrate against him during games.