Single male first to sprint into pool for dip (7)
I believe the answer is:
immerse
'dip' is the definition.
(I've seen this before)
'single male first to sprint into pool' is the wordplay.
'single' becomes 'I' (one).
'male' becomes 'm' (common abbreviation).
'first to' suggests taking the first letters.
'into' indicates putting letters inside.
'pool' becomes 'mere' (mere can mean a lake).
The first letter of 'sprint' is 's'.
's' put within 'mere' is 'merse'.
'i'+'m'+'merse'='IMMERSE'
'for' is the link.
(Other definitions for immerse that I've seen before include "Baptise" , "Dip under the surface of a liquid completely" , "duck" , "Engage deeply" , "dive" .)