Illegal contact penalties in the NFL have tripled this season compared to the same period last year, a largely unnoticed factor among those fueling a record-setting start for offenses.

There have been 24 such flags thrown this season, compared to eight in Weeks 1-4 of 2017. Officials penalized teams only 38 times for illegal contact during the entirety of the 2017 season, prompting league officials to make it a point of emphasis for 2018.

In general, illegal contact refers to contact that occurs before a pass is thrown by a quarterback in the pocket. Officials use pass interference for contact that happens when the ball is in the air.

According to instructions sent to all 32 teams this summer, the NFL emphasized that "a defender cannot initiate contact with a receiver who is attempting to evade him" beyond 5 yards of the line of scrimmage. Incidental contact is permitted, but the league said that "a defender may use his hands or arms only to defend or protect himself against impending contact by a receiver."

The penalty for illegal contact is 5 yards, but awareness of increased enforcement can affect and ultimately diminish the way players defend the pass. Leaguewide passing statistics for completions (2,999), completion percentage (65.4 percent), net passing yards (32,215), touchdown passes (228) and passer rating (94.5) are all the highest they have ever been through four weeks of any season.