Thirteen break out: criminals at last practise Buddhism? (6,5)
I believe the answer is:
bakers dozen
'thirteen' is the definition.
(synonyms)
'break out criminals at last practise buddhism?' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'at last' indicates one should take the final letters.
'practise' becomes 'do' (synonyms).
'buddhism?' becomes 'Zen' (Zen is an example).
The final letter of 'criminals' is 's'.
'break' is an anagram of 'baker'.
'baker'+'s'+'do'+'zen'='BAKERS DOZEN'
(Other definitions for bakers dozen that I've seen before include "Unlucky number of loaves?" , "Additional fare here" , "It might be a bloomer" , "Maybe rolls" , "13" .)