Club that chap joined to go swimming (5)
I believe the answer is:
bathe
'go swimming' is the definition.
(I've seen this before)
'club that chap joined' is the wordplay.
'club' becomes 'bat' (I've seen this before).
'that chap' becomes 'he' (**).
'joined' means one lot of letters go next to another.
'bat'+'he'='BATHE'
'to' acts as a link.
(Other definitions for bathe that I've seen before include "Swim for pleasure, and clean oneself" , "Swim in sea" , "Wash, soak" , "Suffuse" , "Take a swim; envelop" .)