This sobers you up really quickly after a really good win. Bush is the signal caller and communicator for the Steelers defense. Not only that, but his speed and athleticism have been huge for this defense since the Steelers traded up to draft him 10th overall last year.
He is key and really irreplaceable because of those traits in the middle of that defense. It's what the Steelers missed so desperately when Ryan Shazier went down, and now it looks like they'll have to scrap it together for likely the rest of the season.
Backup Robert Spillane came in and had 5 solo tackles, 1 for a loss. Mike Tomlin said after the game that Spillane "more than answered the bell" and is a "capable guy". We'll see just how capable now because it looks like he'll be filling that linebacker role for the rest of the season.
Prayers up to Devin Bush for a quick recovery.