The Cardinals had made it through a good chunk of the season without running into the morass of the pass interference challenges, and then, for two straight games, there it was front and center.

The Tampa game was taken up by two instances right at the end of a close game. Since both were in the last two minutes, those were both about booth review -- coaches couldn't challenge (although Bruce Arians did lose a fruitless challenge a little earlier in the game when one of his guys was flagged for interfering with Larry Fitzgerald.)

But Sunday in San Francisco, there were two instances where Kliff Kingsbury had a chance to challenge. The first came on the very first drive, when Richard Sherman basically dragged down Christian Kirk from behind some 41 yards down the field. No flag was thrown. Kingsbury, wary that PI challenges rarely worked and calls rarely overturned, wasn't sure if he should throw the red hankie. But he did.

When the league office actually overturned the call, making it a 41-yard penalty, "I was shocked myself," Kingsbury acknowledged during an interview on 98.7, Arizona's Sports Station.

Later, linebacker Joe Walker was flagged for a pass interference on 49ers fullback Kyle Juszczyk, a call that looked questionable in real time and horrible on replay. The Cards didn't challenge, and Kingsbury said during his Monday press conference it's a fine line to walk.

"Sometimes those calls are, yes it is pass interference but no it won't be overturned," Kingsbury said. "There is some subjectivity to that that makes it challenging. There is some risk/reward. The deep ball (to Kirk), we thought it was clearly pass interference and we got rewarded with one. The Joe (Walker play) looked close but I didn't feel like we'd get that one. It is challenging but you've just got to do the best you can with it."