Ravens head coach John Harbaugh called his QB's tweet "out of character" on Monday ... and he said he's now urging the Baltimore star to just stay away from Twitter following games.

"It's never going to be positive," Harbaugh said. "It's not going to be a nice place. I think that's kind of reflected in Lamar's response because what he said was just so out of character for him."

"It's not the way he speaks, it's not the way he talks. It's not the words he ever uses. I've never heard him say things like that before."

Harbaugh emphasized that Jackson has the "biggest heart" and that this incident was just a case of his emotions taking over after being trolled following a loss to the Jaguars.

"He's one of the biggest competitors I ever met."