Gary Kubiak asked NFL for clarification on hit that injured Omar Bolden

ENGLEWOOD, Colo. -- Denver Broncos safety Omar Bolden was held out of Monday's practice with sore ribs, the result of a late hit by San Francisco 49ers wide receiver Anquan Boldin.

Bolden was running toward 49ers receiver Torrey Smith, who had just been tackled after a 5-yard completion just before halftime, when Boldin came across and flattened Bolden after the play was over. Bolden was attended to by trainers and then left the game.

Boldin was penalized for unnecessary roughness. Kubiak said he called NFL's vice president of officiating on Monday to see if the play was worthy of more than a penalty as a peel-back type block.

"I was a little confused to be honest with you," Kubiak said. "I talked to Dean this morning about it. We have the rule in place when you're coming back to your goal line how things have to take place. It was described to me as long as it was between the waist and the neck it's OK. They thought the biggest thing there was that it was late."

"When you've got questions with something, you dial them up," Kubiak said. "You don't always like the answers, you know, but you ask. It was explained to me so that's as far as I'll go."

Asked if he thought it was a peel-back block -- a block made on a player who is running in the direction of his own end zone and is ruled as a defenseless player when he is hit by a blocker -- Kubiak said.

"That's a play we're very conscious of in football, any time you've got your players going back toward their goal line we have to coach our players a certain way to block and attack. If anything else it was just a good topic of conversation."