The most common and most likely answer to this crossword clue is the 4 letter word RIGA
I've seen this crossword clue in The Times
R
I
G
A
More clues leading to the result RIGA
- Capital generated in two American states
- Set up a capital — or two states
- Capital equipment beginning to appreciate
- Fix a Baltic city
- Equipment required by a capital city
- Breeze from the south crossing German capital
- A young woman almost flipped somewhere in Latvia
- European capital set up with middle man
- Outfit beginning to accumulate capital
- Capital of Qatar, I gather
Buddy explains!

The straight part
We know that "Capital" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case capital = riga.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.