It may seem as, if in the streaming era, every conceivable football story has already been told. But that’s clearly not the case: here is an uplifting film that has important things to say about racism and empowerment in the game via the life story of Clyde Best, the barnstorming West Ham striker from the early 1970s. Best’s pioneering status as one of English elite football’s first black players is reasonably well-known – but not, of course, as well-known as it should be, which this film sets out to remedy. As well as, of course, the respect he is due for his pathfinder role for succeeding generations of black footballers in the UK.

No doubt that fact is behind the stellar lineup of talking heads who appear on camera to acknowledge the significance of Best’s career, from West Ham contemporaries including Geoff Hurst and Harry Redknapp to those who followed in Best’s tracks, like Viv Anderson, John Barnes, Les Ferdinand, Shaka Hislop and Garth Crooks. Anyone with hazy memories of Best thundering around the pitch from early 1970s editions of Match of the Day will be interested to learn of his remarkable journey to London from Bermuda as a 17-year-old for what was effectively a one-off trial session, after which he was signed by future England manager Ron Greenwood (who, in truth, comes out of this film pretty well). Best says he was quickly accepted by his West Ham teammates, but elsewhere it was less pretty; he found himself at the sharp end of some virulent racism in the post-imperial Enoch Powell 1970s, and it’s sobering to realise that when Alf Garnett yells gruesome abuse from the football terraces, it’s basically Best he is shouting at.

Best wasn’t completely alone. West Ham also had Clive Charles and, a little later, Ade Coker in their squad; when all three were picked for a game against Tottenham in April 1972, it was the first time a top-flight team fielded three black players in the same match – a landmark not to be repeated until the advent of West Brom’s “Three Degrees” in 1978. The film offers a potted history of the English league’s pre-Best black players and, in a footnote, reveals that one of them – Jack Leslie, who banged in dozens of goals for Plymouth Argyle in the 1920s and 30s – ended up cleaning Best’s boots as a West Ham kitman. (Leslie, who died in 1988, appears to have been denied the chance to be the first black England full international in 1925, with suspicions that the selectors withdrew him from the squad after discovering his ethnicity.)

Best ended up leaving West Ham in 1976 to play for Tampa in the original North American Soccer League (NASL), after missing out on West Ham’s epic 1975 FA Cup victory over Fulham. (Best didn’t make the matchday squad, but given football’s naked ruthlessness, it’s perhaps a slightly shakier assertion how much race played a part in his being dropped.) But there’s no doubt of the culture change that greeted him in the US: no monkey chants or National Front, though Coker retells a frightening incident when he got lost in south Boston in 1975 and had to hide from a genuinely menacing mob.

Once Best gets to the US, though, the film’s focus starts to waver away from the man in question, and it metamorphoses into a detail-light encomium for the NASL and its (ultimately futile) attempt to establish itself as a mainstream sport in the US. It perhaps also suggests the uncertain aim of the film itself, caught between appealing to British football nostalgists, selling the modern game to a US audience, and conducting a fervent disquisition on the wider issue of racism in football generally. (That might explain the initially baffling presence of TV actor Tony D Head as the main presenter, who is, shall we say, a little uncertain wrapping his voice around names like Mike Trebilcock and Brendan Batson.)

Be that as it may, Best emerges with considerable dignity, especially with the final montage of his various special appearances and honorary degrees in his elder-statesman guise, and someone with no little appreciation of the importance of blazing a trail. As the man himself says: “My father taught me: ‘Clyde, when you go out there and play, you’re not playing for yourself, you’re playing for the people coming after you.’”

• Transforming the Beautiful Game: The Clyde Best Story is at Sadler’s Wells East from 25 March.