LOTS OF GOOD ONES!"Terific service"
ACE [tennis serves are called "service"]"Gross income source?"
OILGAUGE [I was thinking punctuation]"Conductor whose name is spelled with two musical syllables"
SOLTI"Man of steel?"
BESSEMER [the Bessimer process]"It can make a racket"
CATGUT [some tennis strings are so made; most are man-made]"Where sleeping dogs lie?"
is slang for feet
]"Boxer, e.g.: Abbr."
SEN [Sen. Barbara Boxer]"It's a wrap"
Very clever theme: the answer describes the letter clue as it is used in the answer. I particularly liked FOREGONECONCLUSION for "E" and GRANDFINALE for "D." The only problem is that MALCOMINTHEMIDDLE is not a common expression as are all the others; it's a title. But still, it is most familiar.
What is rapa nui?