The most common and most likely answer to this crossword clue is the 6 letter word MOTORS
M
O
T
O
R
S
Buddy explains!

The straight part
We know that "Moves quickly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case moves quickly = motors.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 MOTORS mean?
MOTORS noun- A machine or device that converts other energy forms into mechanical energy, or imparts motion.
- A motor car, or automobile.
- A source of power for something; an inspiration; a driving force.
- Any protein capable of converting chemical energy into mechanical work.
- The controller or prime mover of the universe; God.
- The fermenting mass of fruit that is the basis of pruno, or "prison wine".
- To make a journey by motor vehicle; to drive.
- To move at a brisk pace.
- To leave.