Break under 50 Ronnie's last - it's unexpected (9)
I believe the answer is:
interlude
'break' is the definition.
(thesaurus)
'under 50 ronnie's last it's unexpected' is the wordplay.
I cannot quite see how this works, but
'50' could be 'l' (Roman numeral) and 'l' is found within the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is located in the answer.
an anagram of 'under' is 'nerud' which is within the remaining letters.
The remaining letters 'ie' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for interlude that I've seen before include "Pause" , "Intermission, break" , "Hiatus" , "Intervening period" , "Eli turned (anag.)" .)