The music once known as heavy metal is suffering a serious identity crisis. In recent years, the genre’s most high-profile media cheerleader Kerrang! has increasingly championed softer forms of rock, notably the more melodic and emotionally expressive “emo” scene with its large and youthful fanbase. As a consequence, it has overtaken its chief rival, NME, in sales. Both publications now target the same readers, cover similar bands and promote themselves with package tours featuring up-and-coming acts.

There was certainly little in the way of traditional heavy rock when the latest Kerrang! tour arrived at Cardiff on Sunday night. Indeed, only the opening act I Am Ghost conformed to familiar genre clichés with their Gothic image and baroque sound. Alas, the Californian sextet also drew the short straw and played to a half-empty hall.

A slightly larger crowd greeted the next band, the Chicago natives Theaudition. Dressed in suburban-mallrat gear, they played songs that were pleasant enough in a lightly metallic, boy-meets-girl way. But like most emo kids, their polished power-pop proved instantly forgettable as soon as they left the stage.

Confusingly named the Bronx, the third American act on the bill actually hail from Los Angeles. They were also the evening’s most flat-out entertaining spectacle. Despite the singer Matt Caughthran being hobbled by a recent leg injury, the brawny young Tony Soprano lookalike still managed to command the stage with his breakneck bellowing and serial-killer grin.

Meanwhile, his colleagues played an ultra-percussive, rowdy racket in the style of a 1980s hardcore punk band. The overall effect was exhilarating, amusing and refreshingly non-emo.

The only Brits on the tour are the headliners Biffy Clyro, a Scottish trio whose complex song structures and angular guitar solos again owe little to traditional heavy rock. But they were clear favourites with the young Cardiff crowd, who roared along to old and new songs alike. Impressively, many had even memorised the lyric to the band’s choppy and ferociously fast new single, SemiMental, before its release. A clutch of more melodic tracks from their forthcoming fourth album, Puzzle, also went down well.

The influence of Nirvana and the Pixies on the singer and guitarist Simon Neil’s stop-start, loud-quiet, angry-sad songwriting is impossible to ignore, but generally positive. Biffy Clyro played a slick and professional set, which may even provide some pointers to the future of heavy rock — assuming this beleaguered genre actually has a future.

But all the same, the Bronx stole the show with their boorish, brilliantly stupid, bull-in-a-china-shop energy.

The tour continues at Nottingham Rock City, tonight; Southampton Guildhall, Thursday; Norwich UEA, Friday; Manchester Academy, Saturday; Newcastle Academy, Monday; Glasgow Barrowland, Jan 23; Liverpool Academy, Jan 24; Birmingham Academy, Jan 26; London Astoria, Jan 27

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