The most common and most likely answer to this crossword clue is the 6 letter word LANCER
I've seen this crossword clue in The Daily Telegraph
L
A
N
C
E
R
More clues leading to the result LANCER
- Cavalryman, one acting as surgeon?
- Cleaner lacking some energy becomes soldier
- Soldier in 3 sealing a street off
- Cavalryman about, in country road on right
- Soldier’s singular dance
- Soldier needs a way out of northern city
- Cavalryman caught in country road close to Sedgemoor
- Cavalryman seen in northern county town strangely sat out
- Soldier on horse crossing a street in northern city
- Dicky clear about new soldier
Buddy explains!

The straight part
We know that "Cavalryman" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cavalryman = lancer.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.
What does LANCER mean?
LANCER noun- A cavalry soldier armed with a lance weapon