Clint, Natasha, and Tony are all benched due to various injuries (or something along those lines) and Thor is currently off-world. Steve and Bruce, as the Hulk, have to keep fighting alone, while the rest monitor the fights from the tower. While Hulk is good at smashing, he's not exactly great at strategy or taking orders, so Steve is often on his own. Bruce also has the benefit of healing after a transformation, while Steve is having a difficult time healing with each new injury. Everyone is living at the tower.
I believe that I read this on AO3, but cannot be sure. Any attempts at searching that I have made have clearly failed.
This is the best description I can think of, so I really hope someone understands what I'm attempting to explain. Thanks in advance!