I don't understand the meaning of let loose used in the following sentence
It is a feel-good genie let loose every year during the British summer, while cricket provides an echo from Lord’s and other grounds across England.
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The "genie" is a metaphor for the Tennis competition at Wimbledon.
In "let loose" means the same as "set free". In Aladdin, the Genie is let loose from the lamp, and then performs magic tasks. In England, Wimbledon is like a genie that is let loose and makes people feel good every summer.
The metaphor is extended in the next paragraph "Wimbledon uncorked its magic..."