Bosa was penalized 15 yards for unnecessary roughness on the play, which came on Richard Sherman's interception return in the third quarter of the 49ers' 27-10 victory over the Vikings.
Afterward, Minnesota coach Mike Zimmer said he believed the block on O'Neill was a "cheap shot."
Coach Kyle Shanahan defended Bosa, saying that he did not have any intent to injury O'Neill.
"I think people say ‘cheap shot' when somebody gets hit violently and to me ‘cheap shot' means your intent is to try to hurt someone," Shanahan said Monday. "And I don't think he's thinking about that at all.
"That's a normal block in football for a long time. The guy wasn't completely out of the play. It was a guy who could've made the tackle, and Bosa went and hit him. That's a rule. You can't do that right now. You can't hit a guy in that position."
In the spring, the NFL adopted a rule making it illegal for a blocker to initiate forcible contact with his head, shoulder or forearm when his path is toward or parallel to his own end line.
Programming note: NBC Sports Bay Area feeds your hunger for 49ers playoff coverage at 2:30 p.m. Sunday for "49ers Pregame Live," with Laura Britt, Jeff Garcia, Donte Whitner, Ian Williams and Grant Liffmann previewing the NFC Championship Game against the Packers. That same crew will have all the postgame reaction on "49ers Postgame Live," starting at approximately 6:30 p.m.
49ers' Nick Bosa fined by NFL for blind-side block on Vikings lineman originally appeared on NBC Sports Bay Area