Wild boar was once sought in Cannock Chase, until the Medieval huntsmen wiped them all out of existence. It's been theorized that Pig-Man could be a sighting of a survivor, whose ancestors have kept themselves safely entrenched in the forest depths.
But how does that explain the human clothing?
There's a local tradition about werewolves prowling the Chase at full moon. Could the Pig-Man be some kind of porcine cousin? A human being, who turns into a swine instead?
Yet more have pointed out that the military have used (and still use) Cannock Chase for all manner of manoeuvrings. Ruins of Prisoner of War camps, and the attendant German cemeteries, line glades in that forest, not to mention the Barracks Museum up Marquess Drive. Unwary wanderers have heard the shots of the modern army in training amidst the ferns and other foliage.
(And I can personally testify to that, having been surprised by rapid gunfire around midnight up Castle Ring. I don't think my friends and I have ever run so fast, as back to our car that night!)
So what if something more occurred within those bunkers? Experiments perchance, amongst the chemical weapons and other accoutrements of warfare? Is that how Pig-Man came into existence?
Or merely a military scare story designed to keep the children away?