Write illegibly as a result of s-stroke (6)
I believe the answer is:
scrawl
'write illegibly' is the definition.
(I've seen this before)
's-stroke' is the wordplay.
'stroke' becomes 'crawl' (crawl is a kind of stroke).
's'+'crawl'='SCRAWL'
'as a result of' is the link.
(Other definitions for scrawl that I've seen before include "Write untidily" , "Crawls away from bad writing" , "Write hastily" , "Illegible hand" , "Write carelessly or badly" .)