Irritate from the beginning (7)

I believe the answer is:

scratch

I'm a little stuck... Click here to teach me more about this clue!

'irritate' is the definition.
(I know that scratch is a more specific form of irritate)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for scratch that I've seen before include "minor injury" , "Score a surface" , "not much of a handicap" , "Score with a sharp object" , "Improvised" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.