The most common and most likely answer to this crossword clue is the 6 letter word RAIDER
I've seen this crossword clue in The Daily Telegraph
R
A
I
D
E
R
More clues leading to the result RAIDER
- Cavalryman arresting a mosstrooper
- Cavalryman possibly is cut by a marauder
- Attacker’s comparatively quick removing pawn
- One up around front of Argos could be a looter
- One who helps to support resistance marauder
- A horseman put out is an aggressive person
- *Attacker‘s assistant
- Cyclist shot by a bank robber?
- Thief’s assistant stopping luxury car
- Heart of terror when assistant enters as aggressive type
Buddy explains!

The straight part
We know that "aggressive type" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case aggressive type = raider.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 RAIDER mean?
RAIDER noun- One who engages in a raid; a plunderer.
- A person who takes or attempts to take control of a firm against the will of current management by purchasing a controlling interest of stock and acquiring proxies.
- A special forces operative; a commando.
- A warship which is light, maneuverable, and fast-moving.
- A person who uncovers evidence of improper behavior within governmental or private organizations.