According to The Athletic’s Jeff Zrebiec, the Ravens have placed left tackle Ronnie Stanley, tight end Nick Boyle, cornerback Iman Marshall, and linebacker Otaro Alaka on the active physically unable to perform list.
Per today's transaction notice, the Ravens placed TE Nick Boyle (knee), LT Ronnie Stanley (ankle), ILB Otaro Alaka (knee) and CB Iman Marshall (knee) on the active PUP list. They can come off at any time when they're ready to practice.
— Jeff Zrebiec (@jeffzrebiec) July 22, 2021
As Zrebiec points out, players placed on the active PUP list can come off the list and join practices as soon as they are able to.