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When Panthers safety Eric Reid was ejected on Thursday night for a hit on sliding Steelers quarterback Ben Roethlisberger, some Panthers fans cried foul: Just four days earlier, the Buccaneers weren’t penalized at all for a hit on sliding Panthers quarterback Cam Newton. What’s the difference?

According to the NFL, the difference is the hit to Newton’s head while he was sliding was “incidental” and not “forcible.”

In a video distributed today, NFL head of officiating Al Riveron showed the play and said that Buccaneers safety Andrew Adams made only incidental contact with Newton’s head.

“The defender has already committed himself by the time the quarterback begins his slide, and there is no forcible contact to the neck or head area. There is some incidental contact, but this is not forcible contact,” Riveron said.

Determining the difference between “incidental” and “forcible” in the instant that a defensive player hits a quarterback isn’t easy, and sometimes the lines will get blurred. But the NFL says that’s the key distinction to make when determining whether or not a hit on a sliding quarterback is a penalty.