How a slider possibly slips off line (7)

I believe the answer is:

derails

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'slips off line' is the definition.
The answer and definition can be both to do with motion as well as being verbs in their -s form.
Perhaps there's an association between them I don't understand?

'how a slider' is the wordplay.
'how' indicates an anagram (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.

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