Learn something new about coach (7)
I believe the answer is:
retrain
'learn something new' is the definition.
(eg to retrain in a new skill)
'about coach' is the wordplay.
'about' becomes 're' (common abbreviation for 'with reference to').
'coach' becomes 'train' (both can mean to instruct a sportsperson).
're'+'train'='RETRAIN'
(Other definitions for retrain that I've seen before include "Teach (someone) new skills" , "Teach fresh skills" , "Teach skills for a new job" , "Acquire new skills" , "Gain new skills" .)