There's a thin line between genius and craziness.

Boris Becker believes Novak Djokovic must straddle it to play his best tennis.

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The Hall of Famer, who coached Djokovic to six of his 12 Grand Slam championships during their three-year partnership, believes the former world No. 1 plays his best tennis when he's edgy, emotional and exuding "street fighter" spirit.

“I like to see the street-fighter attitude,” Becker said of Djokovic during his Wimbledon commentary for the BBC today. “There’s a fine line – you can’t overdo it. If he breaks the rule then the umpire has to give him a warning.

“He is always standing on the edge of going crazy and bringing his best tennis out.”

Three-time Wimbledon champion Djokovic held match point over Marin Cilic before bowing in the Queen's Club final.

Djokovic's last title came on the grass courts of Eastbourne and Becker believes emotions empower his former charge for a run at another Wimbledon title.

"He has been playing his best tennis since he has come back, starting at Queen’s Club,” Becker told the BBC. “He was tested against Kyle Edmund and the other day by [Kei] Nishikori. But his emotions make him strong. Last year he became too quiet, too content, maybe too complacent.”