The father, a mouthy, aggressive leader – determined to win, destined to fail – promises his boys the world. In return, they’ll do something he never could. By 1984, one of the lads has achieved dad’s dream, taking home a National Wrestling Alliance World Heavyweight Championship belt. By 1993, dad has lost five out of six of his sons. If The Iron Claw wasn’t based on real events, you’d ask for your money back.

Not since Darren Aronofsky’s The Wrestler has a mainstream sports picture worked this hard to make us cry. Hardcore wrestling enthusiasts will know the tragic Von Erich family tale inside out; the rest of us will figure it out as it goes along.

Like all the best sports features, however, Sean Durkin’s film doesn’t necessarily require an interest in the protagonists’ pastime. Durkin’s film is loaded with testosterone and boasts its fair share of brutal body slams and painful choke manoeuvres. But it’s not about what happens inside the ring; it is, instead, the devastating story of a family who forgot to look out for one another.

We begin in 1970s Texas where a young Kevin Von Erich (a tremendous Zac Efron), convinces his father, Jack ‘Fritz’ Von Erich (Holt McCallany), that he’s ready for the big time.

Jack, a retired wrestling champ who wishes he’d done more with his time in the ring, is a successful promoter with World Class Championship Wrestling. Most of the Von Erich boys idolise their old man, and dad has made it his mission to turn every one of them into superstar athletes.

Coming up behind Kevin is David (Harris Dickinson), a talented fighter with a flair for the dramatic. Kevin is a great wrestler, but he struggles with social interactions. David is a natural showman, and so Jack encourages them both to fight together. Meanwhile, a younger sibling, Mike (Stanley Simons), dreams of becoming a professional musician, but Jack won’t allow it.

When Kevin fluffs his chance at a world title, his dad switches things up. First, he focuses his attention on David; next, he enlists Kerry (Jeremy Allen White), the favourite son, to form a tag team with the others. Within time, the mighty Von Erich siblings begin to make a name for themselves.

Their mother, Doris (Maura Tierney), prefers not to be included in the family business. Likewise, Kevin’s girlfriend, Pam (Lily James), wonders how much, exactly, is real in the complicated world of professional wrestling (a fair question which the film never properly answers).​

There is more. Kevin worries about a so-called family ‘curse’ that claimed the life of his eldest brother, Jack Jr, when they were children. Is he imagining things, or are the Von Erich men really cursed? The way Durkin’s film moves in its second half, you wonder if Kevin might be on to something.

Mr Durkin doesn’t cover everything. There was another Von Erich brother, Chris, but The Iron Claw’s writer-director decided not to include him in the final screenplay as he says it was “one more tragedy that the film couldn’t really withstand”.

It’s only after watching this profoundly moving film that you’ll understand Durkin’s reasoning. The Iron Claw packs a powerful punch. The wrestling sequences are masterfully staged, beautifully shot and brilliantly performed.

Away from the ring, however, Durkin does not make things easy for his audience. You’ll barely have time to wrap your head around one harrowing incident when another occurs, then another, and I sometimes worried if the film – undeniably effective, if a little untidy in parts – could bear the weight.

Phenomenal performances help. White is excellent as a tortured young athlete who struggles to communicate the thoughts inside his head. McCallany devotes himself entirely to the role of a toxic patriarch who believes his signature move, ‘the Iron Claw’, to be his most devastating. It isn’t – instead, it is his ability to make his sons feel like they’re never good enough.

Kevin is the only one who questions his dad, and this is where Efron shines. A transformative role, in more ways than one, Efron’s soulful, muscular turn stunned the hell out of me, and the committed Californian has never been as good as he is here. Brace yourself for heartache.

Four stars