How a slider possibly slips off line (7)

I believe the answer is:

derails

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

'slips off line' is the definition.
The definition and answer can be both to do with motion as well as being verbs in their -s form.
Perhaps they are linked in a way I don't understand?

'how a slider' is the wordplay.
'how' is an anagram indicator (I've seen this in other clues).
'a'+'slider'='aslider'
'aslider' anagrammed gives 'DERAILS'.

'possibly' acts as a link.

Can you help me to learn more?

(Another definition for derails that I've seen is " Throws (train) off track".)

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.