Dash off to see son perform in pool? (6)
I believe the answer is:
scrawl
'dash off' is the definition.
(dash off can mean to write quickly)
'son perform in pool?' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'perform in pool?' becomes 'crawl' (eg front crawl when swimming).
's'+'crawl'='SCRAWL'
'to see' is the link.
(Other definitions for scrawl that I've seen before include "write hurriedly" , "Write poorly, bad handwriting" , "Untidy writing" , "Scribble" , "careless writing" .)