He's seen time after time in round after round (4)
I believe the answer is:
otto
'he's' is the definition.
(I've seen this before)
'time after time in round after round' is the wordplay.
I cannot really understand how this works, but
'time' could be 't' (abbreviation) and 't' is found within the answer.
'round' could be 'o' (round can mean a round object) and 'o' is present in the answer.
The remaining letters 'to' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'seen' acts as a link.
Can you help me to learn more?
(Other definitions for otto that I've seen before include "Italian for eight" , "Rose petal oil; Bismarck's name" , "Possibly a German" , "Male German name - a palindrome" , "Preminger or von Bismark?" .)