Evidence following large serpent in a water competition between teams (4,4)
I believe the answer is:
boat race
'a water competition between teams' is the definition.
I can't tell whether this defines the answer.
'evidence following large serpent' is the wordplay.
I cannot really see how this works, but
'evidence' could be 'trace' (trace is a kind of evidence) and 'trace' is found within the answer.
'serpent' could be 'boa' (boa constrictor, type of snake) and 'boa' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for boat race that I've seen before include "West London contest?" , "sporting event" , "Oxbridge contest" , "televised row, perhaps" , "Varsity Putney to Mortlake contest" .)