Hayward elevated for a ball and landed with his leg pinned behind his back. In the aftermath, the forward's leg was seemingly bent in multiple directions. He was ultimately carted off the court.
Many of the players looked away, and the Celtics all huddled together on their bench after the serious injury.
LeBron James offered his encouragement to the opposition, while Dwyane Wade couldn't bring himself to look:
Jason McIntyre of FS1 described the scene, and Yahoo Sports shared additional reactions from the floor:
Paul George, who suffered his own serious leg injury while playing for Team USA, offered his support:
He wasn't the only NBA player to reach out on Twitter:
Hayward's former club, the Utah Jazz, also sent their condolences to the injured Celtic:
Players in other sports also reacted to Hayward's injury:
Bryan Fischer of Athlon Sports praised the forward's ability to remain calm after the incident:
Dan Carson provided the closest thing to a silver lining possible after the play, believing Hayward was well-equipped to eventually bounce back from the injury:
The Celtics now face the prospect of playing their season without their marquee free-agent addition. While they still have a number of other talented pieces, such as Kyrie Irving and Al Horford, toppling the Cavaliers in the Eastern Conference now will be all the more difficult.