A big topic of the offseason was the NFL’s elimination of the hip drop tackle, a dangerous play that had led to some high-profile injuries.

The problem may be that it is difficult for referees to recognize in real time what a hip drop tackle is.

There were some plays that were not called that looked like hip drop tackles. Buffalo Bills quarterback Josh Allen thought he was the victim of such a tackle in Week 1 and argued with the refs but did not receive a penalty. Cincinnati Bengals receiver Ja’Marr Chase argued with the refs after a tackle and received a 15-yard penalty, and he may have been upset that a hip drop was not called. Chase did not comment after the Bengals’ loss to the Kansas City Chiefs.

And the play that injured Houston Texans running back Joe Mixon on Sunday night looked like a play that the NFL would penalize this season.

Mixon was pulled to the ground by Chicago Bears linebacker TJ Edwards, his foot trapped under him in what looked like a typical hip drop tackle. Mixon limped off the field and was taken to the locker room. But no flag was thrown.

It’s hard to watch this play and not think it was the illegal hip drop tackle. Both NBC commentators on Sunday night’s broadcast were convinced of that.

“When you wrap, both legs swing off the ground and into the back of the leg,” said NBC color analyst Cris Collinsworth.

“Wrap, twist, weight shift, landing on the feet,” continued live commentator Mike Tirico. “Those are all four indicators that make up this hip drop tackle that they want to take out of the game. All four indicators were there on this play. It’s so hard for the refs to call a penalty live on the field. But something that can be penalized later in the week.”

Given the speed of the game, it’s difficult to see all the mechanics of a hip drop tackle. But it was put into the rulebook for a reason, and referees need to be able to spot it when it happens. It wouldn’t have helped Mixon and his injury, but maybe it would prevent it in the future, which was the NFL’s intent.