The hit is a pretty clear violation of the NFL’s rule “Impermissible use of the helmet.” Here’s how that is outlined in the 2023 NFL rulebook (emphasis added):

ARTICLE 10. IMPERMISSIBLE USE OF THE HELMET. It is a foul if a player:(a) lowers his head and makes forcible contact with his helmet against an opponent; or(b) uses any part of his helmet or facemask to butt or make forcible contact to an opponent’s head or neck area.

These provisions do not prohibit incidental contact by the mask or the helmet in the course of a conventional tackle or block on an opponent. Penalty: For impermissible use of the helmet: Loss of 15 yards. If the foul is by the defense, it is also an automatic first down. The player may be disqualified.

Beckham was not penalized on the play, and Joseph was clearly not happy about that, posting this to his Instagram after the game.

In addition to Beckham, ravens linebacker Roquan Smith was fined for a hit on Jared Goff in the fourth quarter. Smith contacted Goff high and received a 15-yard penalty on the play.