What we know about Damar Hamlin's condition

NFL teams will return to practice today, two days after one of the scariest moments in sports history. Players and coaches are in uncharted waters as they prepare, somehow, for football.

What we know: Bills safety Damar Hamlin suffered a cardiac arrest on Monday night in Cincinnati after taking a hit to the chest during a routine tackle, causing him to collapse.

• Medical personnel gave Hamlin oxygen and administered CPR and an automated external defibrillator (AED) to restore his heartbeat before an on-site ambulance whisked him away.
• He needed to be resuscitated once on the field before being transferred to the University of Cincinnati Medical Center, the Buffalo Bills tweeted.

The latest: Hamlin "remains in the ICU in critical condition with signs of improvement noted yesterday and overnight," the Buffalo Bills said in a statement Wednesday.

• "He is expected to remain under intensive care as his health care team continues to monitor and treat him," the Bills said.

On Tuesday night, Hamlin's uncle Dorrian Glenn said his nephew was still on a ventilator but that he'd improved to 50% oxygen after needing 100% oxygen.

• The Bills-Bengals game will not be resumed this week, and the NFL "has made no decision regarding the possible resumption at a later date."
• The Week 18 schedule remains unchanged — for now.

What they're saying: Cardiologists are hesitant to speculate on what happened to Hamlin, but many experts say he likely experienced commotio cordis, a rare event caused by a blow to the chest wall.

• If the impact happens during a "brief, vulnerable moment in the heart cycle, it can cause the heart to go out of rhythm and basically stop," Scott Jerome, a cardiologist at the University of Maryland Medical Center, tells Axios.
• Fewer than 30 cases are reported every year, per the National Library of Medicine. Jerome says most sports-related occurrences involve objects like baseballs and pucks.
• "It's usually little league catchers getting hit with a pitch ... hockey players getting hit with a shot," he said.

Between the lines: An NFL stadium is one of the safest places Hamlin could have suffered a cardiac arrest. Time is absolutely critical, and trained emergency personnel were just steps away.

• The NFL has an emergency action plan for every stadium, and the ~30-person team at Paycor Stadium was fully prepared. Jerome hopes their response in those surreal moments inspires others to learn CPR.
• "Everybody should know CPR, and there should be an AED everywhere," says Jerome. "The CPR circulates the blood while the heart's not beating, and the AED — the shock — is what saves you."

The big picture: Hamlin's fundraiser for a Pittsburgh-area toy drive has become a vessel for humans to show another human love and support.

• Since Monday night, 200,000 people have donated nearly $6 million.

Go deeper: Bills-Bengals game won't resume this week, NFL says, as Hamlin remains in critical condition

Editor's note: This story has been updated with additional developments.