The San Francisco 49ers may have mopped the floor with the Oakland Raiders on Thursday night, riding a surprise debut from quarterback Nick Mullens (who?) to beat Jon Gruden's team by 31 points.

But they also lost one of their most significant contributors, and they lost him in an ugly way.

Raheem Mostert had been one of the Niners' few offensive bright spots in recent weeks, relieving banged-up running back Matt Breida, who, in turn, has been replacing Jerick McKinnon, who suffered a torn ACL before the season. The former undrafted Purdue product may have had a career performance through almost three quarters of Thursday's game, too, averaging almost 13 yards per carry and scoring on a 52-yard sweep.

Mostert's night will probably be remembered more for how it ended, however, and it did not end well.

With just under five minutes to play in the third, Mostert took an inside hand-off and was tripped by a Raiders defender. As he fell to the ground, he tried using his right arm to brace the fall, only to have his forearm completely fold in half -- a gruesome break during which Mostert's screams could be heard over the Thursday night broadcast. Players on both sides of the ball immediately and repeatedly beckoned for medical attention on the field, which indicated the severity of Mostert's injury before any replay was shown, and close-ups of the Raiders sideline showed players like Jalen Richard wincing at the sight of the accident.

Video of Mostert's injury, which figures to sideline him for the remainder of the season, is graphic, so viewer discretion is advised: