A talk hosted by leader in sport (8)
I believe the answer is:
kayaking
'sport' is the definition.
(kayaking is a water sport)
'a talk hosted by leader' is the wordplay.
'talk' becomes 'yak' (yak is a kind of talk).
'hosted by' indicates putting letters inside.
'leader' becomes 'King' (a king is a royal leader).
'a'+'yak'='ayak'
'ayak' placed inside 'king' is 'KAYAKING'.
'in' acts as a link.
(Other definitions for kayaking that I've seen before include "sport" , "Travelling in a small canoe" , "Operating canoe" .)