Reserve team up to take a dive? (8)
I believe the answer is:
submerge
'take a dive?' is the definition.
'reserve team up' is the wordplay.
'reserve' becomes 'sub' (I've seen this in other clues).
'team up' becomes 'merge'.
'sub'+'merge'='SUBMERGE'
'to' acts as a link.
(Other definitions for submerge that I've seen before include "Engulf, immerse" , "Cover" , "Put under water" , "Sink - inundate" , "swill round" .)