let loose

1 :  to allow (someone or something) to move or go freely He let the dogs loose in the courtyard. cattle let loose to graze on the green fields —often used figuratively a director who's willing to let her actors loose to interpret their roles however they see fit how to stop the violence that has been let loose on the city

2 :  to produce (something, such as a cry) in a sudden and forceful way The crowd let loose an enormous groan when the pass was intercepted. She let loose (with) a scream.