I hate to state the obvious, but keeping him in would be the best thing
anyway

Well, if you see the balck cat yourself you could try hasing it away with a
spray of sticky orange juice ( they dont like it as it takes ages to get off
their fur - but it doesnt harm them) My vet told me that one when my very
ill little cat was being bullied by ( a black) cat.

Its not lways possible to keep them in, even my  poorely little boy liked to
sit out on the patio.
Ive chased off cats several times for him.

In the end though, he did have to fight ( and won) the black cat didnt come
back

Do you know who the black cat belongs to? If you do you might talk to the
owner and ask if they could keep their kitty home.  Tell them that he is
injuring your cat on your property.

If it's a stray you could trap it (as long as you're sure it's a stray) and
turn it over to a rescue group. I'd check with the rescue people before
trapping it to make sure they can take it then.

You might consider building a fenced enclosure where Scamp can enjoy the
fresh air without meeting up with Mr. Black Cat Bully.

Or you could keep Scamp inside. They do get a little older and slower and
start losing the fights they used to win.

A large black cat has been coming into my yard and beating up my white
fixed male, Scamp.  Scamp tries to chase it away and sometimes it just
jumps him. This last time I had to take Scamp to the vet for his
injuries. Any solution besides chasing the black cat away? Scamp BEGS to
go out but I've kept him inside as he is still healing.

Just to add that until the black cat is controlled, captured, or driven away
permanently, don't clip Scamp's claws. Scamp needs long, sharp claws not
only to defend himself with, but also for climbing to safety with, and even
as tools with which to drive the black cat away.