Lions rookie cornerback Terrion Arnold being evaluated for injury after big hit

Depending on the Lions' reporter who kept tally and is cited, there were either eight or 10 fights during Monday's joint practice between the Detroit Lions and New York Giants. There were a couple noteworthy hits too, including one by Lions undrafted rookie defensive back Morice Norris.

Two Lions players emerged from Monday's session banged up. According to the team, via multiple reporters, guard Kevin Zeitler is being evaluated for a shoulder injury. The co-headliner is rookie cornerback Terrion Arnold, who is being evaluated for a concussion.

Arnold left practice after taking this big hit from Giants left tackle Andrew Thomas on a perimete run play. Arnold somehow never totally lost his footing, and he even lowered his shoulder to take on the hit. The sound captured by Ralph Vacchiano of Fox Sports reflects the intensity of the hit.

Giants have a big question to answer about Andrew Thomas after hit on Terrion Arnold

It might be easy to miss on a first (or even a second) viewing, distracted by the sheer sound of the hit, but a reply on Twitter to Jeremy Reisman of Pride of Detroit asked a pertinent question:

Where is Thomas' Guardian Cap? He seems to be the only player on the field who was not wearing one, and it feels certain he was.

As Reisman passed along after pulling it from the news that players will be allowed to wear a Guardian Cap during games starting this season, the Giants have some explaining to do.

Here's the applicable passage of that news item.

"The NFL instituted Guardian Caps during training camps ahead of the 2022 season, and then they were mandate during the 2023 season at every preseason practice, as well as every regular-season and postseason practice with contact. Players at position groups where head contact is seen most are required to wear the Guardian Cap, with running backs and fullbacks joining the previously included linemen and linebackers. The only positions not required to wear the caps are kickers, punters, quarterbacks, wide receivers and defensive backs."

There's no exemption for a player not liking to practice in a Guardian Cap all the time from a comfort perspective, or hot weather conditions providing an exemption in that way. So why wasn't Thomas wearing one? It was probably a mistake or an oversight and nothing more, but Reisman dove a little deeper.

Per a team source:

"There are five or six helmets that test better than the guardian cap and he wears one of them. If you wear a helmet that tests better then you don’t have to wear it. You can wear but you don’t have to"
-Jeremy Reisman, Pride of Detroit (on Twitter)

So Thomas' helmet apparently tests better than the Guardian Cap, so he doesn't have to wear one if he doesn't want to. It doesn't make it right that he didn't, if only to protect a player he might collide with, but there's a loophole that the Giants and their left tackle took full advantage of.

Hopefully Arnold is not dealing with a significant head injury. But it's fair to assume he won't be participating in Tuesday's joint practice.