Again tries to practice endlessly (7)
I believe the answer is:
rehears
'again tries' is the definition.
('hears' can be a synonym for 'tries' so perhaps 'rehears' is OK for 'again tries')
'practice endlessly' is the wordplay.
'practice' becomes 'rehearse' (synonyms).
'endlessly' means to remove the last letter.
'rehearse' with its final letter taken away is 'REHEARS'.
'to' is the link.
(Other definitions for rehears that I've seen before include "judges over" , "Once again tries" .)