Sink U-boat team? (7)
I believe the answer is:
subside
'sink' is the definition.
(I know that subside is a kind of sink)
'u-boat team?' is the wordplay.
'u-boat' becomes 'sub' (German submarine).
'team?' becomes 'side' (both can mean a sports team).
'sub'+'side'='SUBSIDE'
(Other definitions for subside that I've seen before include "Fall back" , "Sink, settle" , "Go down in level" , "Sink to a lower level" , "Wane" .)