backbiting of a coward; grumblings of a loser
Idiomatic expression describing someone who, after losing or retreating, complains or criticizes from a safe distance. The literal image is 'the distant bark of a defeated dog'.
His backbiting is nothing but the grumblings of a loser.
There's no need to listen to the coward's distant barking.
負け惜しみ refers to being a sore loser or making excuses after losing, while 負け犬の遠吠え specifically implies criticizing or complaining from a safe distance after defeat.
遠吠え alone means 'howling in the distance' or 'distant barking', but the full idiom 負け犬の遠吠え carries the figurative meaning of cowardly backbiting.
The expression is a set phrase combining 負け犬 (defeated dog) and 遠吠え (distant barking), literally meaning 'the distant bark of a retreating dog'. It figuratively describes cowardly complaints made after a loss.