50 accommodated in Massachusetts do break down (11)
I believe the answer is:
malfunction
'break down' is the definition.
(malfunctioning is a kind of breaking down)
'50 accommodated in massachusetts do' is the wordplay.
't0' becomes 'l' (Roman numeral).
'accommodated in' indicates putting letters inside.
'massachusetts' becomes 'ma' (abbreviation).
'do' becomes 'function' (both can mean an event).
'ma'+'function'='mafunction'
'l' put into 'mafunction' is 'MALFUNCTION'.
(Other definitions for malfunction that I've seen before include "Break down" , "Fail" , "Go wrong" , "Failure (of equipment)" .)