To answer the title of the thread, "I'd say whatever he can," which may involve some creativity. As I type, RipkenFanson is throwing a ball up against a school wall. He has also run sprints or laps where possible and dug out his weighted vest from somewhere tucked in his bedroom. But here's the creative part- he's converted our garage into a personal gym.
He took three heavy cloths that we got when we moved here (that ensured that furniture wouldn't get scratched). found clamps and hung them in the garage. This provided him with a "screen" to practice tee work. Then he is using a board that my late father- in- law used to paint. This board was strong as my father in law had placed between it two ladders. This became son's workout bench, which rests on two containers that we had of baseballs. Then he fastened two poles together (I think one was used for Christmas lights and the other was a former broom handle that I used to unclog the lawnmower) to make a bar for weights that he clamped on the end. Additional weights are from empty buckets from cat litter that he fills with sand and or water (he was explaining to me something about the density). Good to have him back and make use of a tough situation.He also has a mat and place to hang towels.
He was proud of his contraptions, enough to call his GF after 11:00PM on a school night for her. He told me some of his creations deserve more attention for his "special box" (memorabilia) than old newspaper clippings. The garage has never been so musical (thanks Big Blue party). As a byproduct of his handiwork, his mom and I are glad the garage got cleaned up.
He actually laughed when I peaked in the door and quipped, "It's nice to see you finally using your major!" (engineering).