Answer: fourminutemile

AnswerCrossword Clue
FOURMINUTEMILEWhat Bannister broke
FOURMINUTEMILERoger Bannister first broke it
FOURMINUTEMILESports barrier broken in '54
FOURMINUTEMILEBroken record.
FOURMINUTEMILERoger Bannister feat
FOURMINUTEMILEBannister achievement of 1954